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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Helping son with cam break in for a 1986 IROC LG4 305. Stock CCC Rochester which we rebuilt and had functioning properly before engine teardown. Project has spanned last year as we fully restored the chassis, motor, rear diff and interior. We had engine components reconditioned at machine shop, clean hone, head job and we reassembled motor with new chain, oil pump etc. We installed a comp cam RV type cam which was mild enough that spring upgrade was not recommended by Comp Cams. We degreed in the cam and confirmed all specs and TDC location.
All cooling system/ignition components are new and had been run before disassembly of the motor about 8 months ago..
We set base timing at 10 degrees advance..
Car fired right up but after 7 to 8 minutes of break in at 2000 to 2500 rpm, started to overheat. We suspected the new thermostat (195F) so we replaced with a second new stat which we tested in kitchen when we replaced. I think the original was hung up. Original was Gates brand and had a rubber seat. The replacement NAPA/Belkan (195F) we swapped in was all metal, no rubber. After fiddling with the Gates in the kitchen, we agreed it was working but not sure if it was hung up in the car before we removed.
We had gone through three break in runs that lasted about 5 to 7 minutes each before boil over before we replaced tstat. All between 2000 to 2500 rpm. Each time trying to debug the cooling with different ideas.
We had jumped the electric fan after second overheat so it is 100% on. We also ran the interior heat after 2nd overheat and we get good hot air through the dash (this is highest point in system and not air blocked).
When we finally swapped the tstat and then carefully topped of the cooling system (filled radiator and observed coolant up to the tstat manifold housing connection then installed the tstat) and we got our longest run of ten minutes before it started to boil (but not as violently). We did observe the tstat opening as the gauge went up to 220 then dropped to 160 abruptly, Then it floated back up to 220 then held for a while before it climbed to 240 before we shut it down. On the last run, we lost no coolant through overflow and we carefully filled the reservoir as the car sucked down on it. The reservoir sits at full cold level this morning.
Exhaust looked/felt good. No black soot.
We looked at the SES codes and we only have code 24 which is the VSS speed error. Apparently this sets when car is 0 mph, 1500 to 2500 rpm (exactly what we were doing at cam break in). The problem is that I understand that the VSS error will impact the timing circuit.
We decided that after the cumulative 25 minutes at 2000 to 2500 rpm, the cam/lifters are broken in. Motor sounds good so I think we have no issue there. We now want to set the timing at idle and adjust the curb idle and start the process of breaking in the rings. We dropped the first load of break in oil as recommended to us and dropped the filter and installed another fill of break in oil and new filter. Used oil looked good with some metal presumable from the break in but no sign of coolant ingress and volume removed was almost (but not more than) the full five quarts. We cut open filter and observed some metal. Again presumed to be result of cam/tappet break in.
So, my questions are as follows:
1. Would the VSS error code change the timing advance and could this have contributed to the overheat conditions?
2. When breaking in the cam, are we supposed to have the distributor advance circuit enabled or disabled? We had tried a few runs with the two wire connector under the wiper motor connected and also disconnected. We saw no difference in the running at 2000 to 2500 nor did it changed the overheat condition.
3. We always had the 4 wire connection on the distributor connected. Was this supposed to be disconnected instead?
4. How should the timing circuit wiring be configured for setting the timing and curb idle. (two wire disconnected, four wire disconnected, both connected?)
My older brother is a professional and experienced (60 YO) mechanic and he is concerned there could be a bigger issue with the motor as he has never had such an overheat problem breaking in countless SBC motors in his career. But he does not recall all the nuances of the CCC Rochester circuits (he forgot more than most will know) so I am researching the VSS and timing issue on this forum with those who may be more current. The NAPA guy (my friend) is concerned the water pump could be faulty. It is Gates and I confirmed the part number is correct for the car (std rotation).
I have no more ideas as to the issue of the overheat. My son feels it is a result of the tough duty of running 2000 to 2500 at standstill. It was a cold day last two days (40f ambient) in NJ while we did this.
Looking for any assistance before we move ahead. Don't want to replace water pump (or pull heads!!) if we are missing something dumb or the overheat is normal on these motors during break in of a cam.
Think I've herd too little advance can increase the heat on break in, someone suggest using a locked dist just for break in, I've been fine either way.
Stopping n starting the break-in is fine to fix issues, still not ideal if you were getting hot as the reason.
I always use a box fan to help cool n jack up the front a bit if needed(depends on vehicle but does seem to also help with trapped air bubbles).
Some fine magnetic metal is normal, I get metal in the filter using a filter magnet on my daily 2009 4.3 Silverado.
Thank you for the feedback.
Here is the current status:
Complete new cooling system other than the electric fan.
Radiator
Heater Core
Tstat (actually put second one in and test both in the house to make sure they open.)
New 16 psi cap
Water Pump
Hoses.
All parts were purchased at Rockauto.
Car has been cycled several times and overflow tank has been topped off and car has sucked down to full cold (I expect therefore minimal if any air).
The fan switch was jumpered to run full time.
Heat was turned on to give margin (plus it was cold here) and the heat blows hot.
We tried spec timing setting (0 deg BTC at 700 RPM) but motor did not like that. No longer stock cam. We now have a comp cams mild RV cam.
We advanced timing to 10 deg BTC at 700 RPM and motor smoothed out somewhat.
We took car for a short drive with EZ throttle keeping RPMs below 2500. Car held 220 deg on the dummy gauge for about five minutes or so. Then it picked up to 230 and held for a while.
Then it crept to 240 and above and we pulled in driveway and shut it down.
Popped the hood. Upper hose was hard and hot, but the radiator cap did not lift. Reservoir was inch or so above the full hot line, but no bubbling through the vent.
Scratching our heads.
Timing is set at 10 deg BTC at 700 RPM with 4 pin connector disconnected.
Sorry, I had a typo in the reply post. I stated heat was blowing cold. That was a brain fart. We have good heat in the car with the fan on and selector set to heat.
I am questioning the new radiator and possibly is the water pump defective. New Gates Water pump from Rockauto. The new radiator seemed to match the old radiator which was very old and had signs of weepage as car was not running for several years.
Well another thing to check is your temp gauge. My neighbor had a hard to find problem with a new pump, hot the tolerances changed enough for the pump impeller to slip but cold it was fine.
Are you sure that you have the correct rotation water pump?
edit: Also make sure the bottom hose isn't sucking shut with RPM, does it have the coiled wire inside?
Good comments. The car takes a standard rotation water pump vs reverse rotation for the newer model camaro with serpentine. I can confirm I got the right box, but whether the pump in the box from Rockauto was right, don't know. It did not look tampered with when I received it.
The lower hose did not have the coil in it, but I do not see it collapsing under higher RPM.
I am suspicious that the distributor might be screwing up the timing advance. I have all new AC Delco components, but it could be screwed up just the same.
I was looking for an excuse to get an infrared temp gun, now I have it. Good suggestion.
But, I think the water neck is the temp that goes to the ECM. The temp gauge is the sensor near cylinder number 1 on the driver side head. Would the two temps be very different?
The temp switch on the passenger side head by dypstick/cylinder 6 is for the cooling fan on/off switch.
Good suggestions from others - here's a couple more:
While cold/cool, can you see flow in the radiator with the cap removed? If so, then WP is good.
The stock gauges are not much better than a dummy light - not accurate at all and not linear. Seeing 240 is almost normal.
You could try to disable the fans and run cold garden hose water over the radiator for a comparison.
Advance the timing even more, like 16 degrees at idle with 4 pin connector disconnected.
As long as the engine is not trying to kick back while starting, you're good.
What you are experiencing is exactly why I break my engines in on a test stand with a "dumb" mechanical advance distributor and manual carb.
Last edited by NoEmissions84TA; 01-28-2023 at 05:30 PM.
Here is what I think we know regarding timing......
We set the curb idle at 700 rpm with the 4 wire harness disconnected to 10 degrees advanced. This was Comp Cams suggestion for the cam we put in. The GM sticker on the the hood wants 0 degrees at 700 rpm but the car struggled there.
We then connected the 4 wire harness to check the distributer spark advance....if we did it right and will double check in the morning, we needed to adjust the timing gun to about 40 degrees advance at idle to get the balancer mark on the pointer, and then over 50 degrees to get the mark on the pointer between 2500 and 3000 rpm.
It seems the timing advance is screwed up (understatement).
Those timing numbers sound correct.
Remember, the timing advance is all electronic.
During break-in, you are at 2500 rpm (full or nearly full "centrifugal" advance).
Plus no load on the engine at what the ECM thinks is a downhill cruise on the highway (full "vacuum" advance).
Add the initial timing to that and you can indeed see 60 degrees on the timing light.
But, I think the water neck is the temp that goes to the ECM. The temp gauge is the sensor near cylinder number 1 on the driver side head. Would the two temps be very different?
The point is to get an independent reading of the temps. If you're seeing something like 170-190 at the water neck, radiator, wherever, and your temp gauge is showing 240+, that's a suspicious difference. Plus you can point the temp gauge wherever you want, I just like to pick the water neck because it's easy to hit and if it is somewhat close to the temp you're seeing on the gauge, then it's more likely we're working with a real overheat scenario.
So, 40 degrees advanced curb idle timing at 700 RPM seems correct based on 10 degrees when the 4 wire is disconnected?
I was less concerned about the 50 degrees at 3000 rpm because it would be 40 more than the base 10.
Does reading 40 degrees advance at curb idle seem way to high?
Just want to be sure I understand your reply.
Yes, that sounds about right. Set base timing at idle with distributor plug disconnected. It’s been a while since I had an LG4, but I believe you do disconnect the 4 wire connector on those. When you reconnect the plug, the timing will advance a lot (30-40 degrees advanced at idle under no load is typical).
If you were setting base timing with the distributor plug connected, the timing would end up being retarded. That could cause it to run hot and not have much power.
even with the EST disconnected at the dist, the ICM will still add some timing around 1500ish rpm, as a limp home feature.
with the EST connected the ECM will add timing at idle and you'll see a good 25ish degrees of advance at idle.
10 degrees base with the EST connected is likely too much. 0-4 degrees base is a good starting point.
running rich or lean can also cause over heating.
Any condition that keeps the motor from operating efficiently results in more heat. Spark too soon and the motor is fighting itself, spark too late and the charge is still burning after work is done. Lean or rich mixtures (among other things) affect the burn rate, which comes back to timing.
I'd start at base timing of 0 degrees, leave everything connected letting the ECM command timing. Make sure the ccc-qjet is metering fuel correctly, they can get 'gummed' up from sitting.
Does the MCS click? Do you measure 1/8" of travel for the MCS plunger through the IAB port?
The ccc-qjet will most certainly need some adjustment for the new cam but if functioning correctly shouldn't overheat right off.
The stock cooling system should be easily capable of controlling temps.
In my experience the reverse rotation water pump will not bolt in place of the standard rotation water pump and allow the V belt accessories to be installed. They have different mounting bosses for the drives. I'm not sure how anybody could mix them accidentally, if using a stock accessory drive anyway. But hey, stuff happens.
We pulled all the plugs and all eight had a white burn. I assume this means leaner than richer burn? Pictures don't do it justice, they were whiter than the pics.
Cylinder 1, 3, 5 & 7. 2-4-6-8 were similar
Cyl 3 Cyl 5 Cyl 7 Cyl 1
We checked the balance mark against the timing marks and the distributor installation no issue. I was pretty much certain that would be the case as I degreed the cam with a degree wheel when the motor was assembled and the cam specs, Cylinder 1 TDC and the Balance Mark and timing cover pointer were all verified.
So after all of that, we swapped water pumps. I removed the new gates pump and put in a car quest advanced auto heavy duty pump. We opened up both pumps to study the impeller. Both were eight vane, but the heavy duty auto zone pump had a backing plate, which would make it much more efficient as there would be more pressure and less slip/bypass. Both pumps were std rotation as required so issue there.
We refilled the system and per the GM service manual, topped off the system and waited for the tstat to open. It did and we filled system, capped it and put coolant in the overflow.
We still had the electric fan jumpered to 100% and the car was running very cool (sub 200 on the gauge). We took it for a ride. Had reasonable heat from the dash and everything seemed good. We stopped and un jumpered the fan and put it to the head temp switch. Continued driving gingerly to see what would happen. The temp started to creep up to 260 after about 5 minutes and we could tell the car was running hotter. We went straight to the driveway and shut it down The overflow had risen but the car was not boiling through the vent cap. Also, the fan was on when the key was engaged so the fan temp switch was working (whether it works correctly, don't know). The car was definitelky hot, because it did not want to cranks/start in the drivewayu.
I am now wondering if we have a lean burn condition.
I will back off the timing some tomorrow as suggested by others and jumper back the fan and see what happens.
I am investigating what I can do to richen the carb right now.
We pulled all the plugs and all eight had a white burn. I assume this means leaner than richer burn? Pictures don't do it justice, they were whiter than the pics.
Cylinder 1, 3, 5 & 7. 2-4-6-8 were similar
Cyl 3 Cyl 5 Cyl 7 Cyl 1
We checked the balance mark against the timing marks and the distributor installation no issue. I was pretty much certain that would be the case as I degreed the cam with a degree wheel when the motor was assembled and the cam specs, Cylinder 1 TDC and the Balance Mark and timing cover pointer were all verified.
So after all of that, we swapped water pumps. I removed the new gates pump and put in a car quest advanced auto heavy duty pump. We opened up both pumps to study the impeller. Both were eight vane, but the heavy duty auto zone pump had a backing plate, which would make it much more efficient as there would be more pressure and less slip/bypass. Both pumps were std rotation as required so issue there.
We refilled the system and per the GM service manual, topped off the system and waited for the tstat to open. It did and we filled system, capped it and put coolant in the overflow.
We still had the electric fan jumpered to 100% and the car was running very cool (sub 200 on the gauge). We took it for a ride. Had reasonable heat from the dash and everything seemed good. We stopped and un jumpered the fan and put it to the head temp switch. Continued driving gingerly to see what would happen. The temp started to creep up to 260 after about 5 minutes and we could tell the car was running hotter. We went straight to the driveway and shut it down The overflow had risen but the car was not boiling through the vent cap. Also, the fan was on when the key was engaged so the fan temp switch was working (whether it works correctly, don't know). The car was definitelky hot, because it did not want to cranks/start in the drivewayu.
I am now wondering if we have a lean burn condition.
I will back off the timing some tomorrow as suggested by others and jumper back the fan and see what happens.
I am investigating what I can do to richen the carb right now.
I spent a fair amount of time today confirming all the parameters.
Over the last year, I procured a full set of vintage tools to rebuild quadrajets including the CCC type.
1. The carb has a new TPS and per the factory manual, it measures 0.54V at closed throttle, over 4V at FOT and the sweep is smooth, not choppy.
2. I have the small black float scale and the wet float level measures 11/32 per spec.
3. I set the MCR Lean stop screw with the brass BT Tools Gauge in the throttle side jet.
4. The Rich stop screw was set to achieve 4/32 (1/8) travel per spec.
5. Idle Bleed Air was set with the special gauge tool.
6. Idle screws are set 3 turns out.
1. We did the MCR response check and the RPM dropped over 300 RPM, (actually more like 1000 RPM)
2. If we did the DWELL check properly, it was hunting between 29 deg and 31 degs. I had set that about 9 months ago, when I rebuilt the carb before tearing down the motor.
Full assembled all the air inlet box on the car and kept the electric fan jumpered to run 100% of the time.
We reset the timing to 6 deg advanced as suggested by others.with the 4 pin connecte unplugged The car did not idle as good at 6 deg as it was idling when it was at 10 deg advanced but we put to 6 max as suggested by others on this forum who felt 10 was too much..
I check the curb idle advance with the 4 pin connector connected and we had to dial my timing light to about 42 to hold the zero mark at around 750 rpm.. At 3000 RPM, we had to go to 52 to hold the zero.
We then took the car for a short run to fill the tank. We ran it about 5 minutes/three miles and we did some throttle loading to start seating the rings. It had good response and seemed to pull nice. We also felt the secondaries kick in and there was no noticeble quadrabog (I had replaced the vacuum secondary dash pot last year because the original was opening too slow).
We got to the gas station (three miles/five minutes) and it was running hotter. Shut it down and filled up. It was not boiler over but when we went to start it, it was hot and hard to start.
We drove home (three miles and the gauge crept to 260 (in the red). We pulled in the garage and shut it down. It was not boiling over, but the overflow almost full to the vent cap hot, there was some coolant around the cap (which is a new stant 16 psi lever type cap) and there was some rumbling in the upper hose.
We are at a total loss where to go with this next. I will pull a few plugs tomorrow when I get home from office, but other than that, I am thinking to throw a vacuum distributor and qJet I pulled off a 1979 350 SBC that I knew was running well when I pulled that motor out of the truck last June. Thinking that set up will be richer and want to see if it helps the motor.
I spent a fair amount of time today confirming all the parameters.
Over the last year, I procured a full set of vintage tools to rebuild quadrajets including the CCC type.
1. The carb has a new TPS and per the factory manual, it measures 0.54V at closed throttle, over 4V at FOT and the sweep is smooth, not choppy.
2. I have the small black float scale and the wet float level measures 11/32 per spec.
3. I set the MCR Lean stop screw with the brass BT Tools Gauge in the throttle side jet.
4. The Rich stop screw was set to achieve 4/32 (1/8) travel per spec.
5. Idle Bleed Air was set with the special gauge tool.
6. Idle screws are set 3 turns out.
1. We did the MCR response check and the RPM dropped over 300 RPM, (actually more like 1000 RPM)
2. If we did the DWELL check properly, it was hunting between 29 deg and 31 degs. I had set that about 9 months ago, when I rebuilt the carb before tearing down the motor.
Full assembled all the air inlet box on the car and kept the electric fan jumpered to run 100% of the time.
We reset the timing to 6 deg advanced as suggested by others.with the 4 pin connecte unplugged The car did not idle as good at 6 deg as it was idling when it was at 10 deg advanced but we put to 6 max as suggested by others on this forum who felt 10 was too much..
I check the curb idle advance with the 4 pin connector connected and we had to dial my timing light to about 42 to hold the zero mark at around 750 rpm.. At 3000 RPM, we had to go to 52 to hold the zero.
We then took the car for a short run to fill the tank. We ran it about 5 minutes/three miles and we did some throttle loading to start seating the rings. It had good response and seemed to pull nice. We also felt the secondaries kick in and there was no noticeble quadrabog (I had replaced the vacuum secondary dash pot last year because the original was opening too slow).
We got to the gas station (three miles/five minutes) and it was running hotter. Shut it down and filled up. It was not boiler over but when we went to start it, it was hot and hard to start.
We drove home (three miles and the gauge crept to 260 (in the red). We pulled in the garage and shut it down. It was not boiling over, but the overflow almost full to the vent cap hot, there was some coolant around the cap (which is a new stant 16 psi lever type cap) and there was some rumbling in the upper hose.
We are at a total loss where to go with this next. I will pull a few plugs tomorrow when I get home from office, but other than that, I am thinking to throw a vacuum distributor and qJet I pulled off a 1979 350 SBC that I knew was running well when I pulled that motor out of the truck last June. Thinking that set up will be richer and want to see if it helps the motor.
Your thoughts?
I really doubt air/fuel mixture is the issue here. It is most likely an air pocket or a bad thermostat. Pull the guts out of an old thermostat and use just the body as a restrictor. Install it and see if the issue goes away or persists. I run lean cruise at 17:1 air/fuel ratio and have not had overheating issues. There is actually less heat running leaner because there is less fuel to combust. Any chance your balancer/timing pointer is off. Retarded ignition timing can add a good bit of heat.
I had rebuilt the motor and installed new Comp Cams RV cam and lifters.
The timing cover was rusty and mark was not legible so I installed new identical timing cover (dorman repro).
The Harmonic Balance was original (oil soaked and rubber was cracked) so I bought new replacemrnt.
New Cover and HB were confirmed visually to be identical to old (location of pointer on cover, keyway and timing mark on HB).
I accurately degreed the cam to confirm the cam specs using moroso wheel and a dial gauge on number one piston so I know my timing marks are spot on the #1 TDC. I just reconfirmed the distributor install vs #1 TDC as my mechanic brother was on my case to make sure that tne distributor was installed correct.
The car idles pretty well at idle. Motor seems to prefer 10 degrees BTDC vs 6 degrees BTDC.with 4 pin disconnected. The car will not run with the Hood Sticker spec of 0 degrees BTDC with the 4 pin disconnected.
On a cold start, the car starts right up with no issue. Choke setting is good. I had rebuilt carb 9 months ago before teardown knowing I needed good carb to perform the cam breakin..
As for the TStat, we replaced 1st Tstat that was a 195 degree Gates which had a rubber seat, for a second NAPA Balkan all metal seat. Both were checked in the kitchen in a pan of hot water when we did the swap of the 1st to 2nd tstat. Both opened at 195 degrees (verified by digital thermometer) but I was suspicious that the the 1st Tstat with rubber seat may have been hanging up.
We are sure the Tstat is opening. I can certainly gut the gates Tstat and swap it in, I just think the Tstat is not the issue as we know it is opening and we are running for about 5 minutes on the road before the temperature starts to take off and not subside. As previously stated, we jumpered the electric fan to run 100% of the time so the Fan Temp Switch is not being used./counted on.
Very frustrating as I am out of ideas.
Could the the Distributor 7 pin ICM be defective? It is a` new AC Delco installed with the thermo paste. Could this cause intermittent timing problem while driving, leading to overheat?
We installed 2nd tstat and 2nd heavy duty water pump and radiator and heater core are new. All hose new.
block and heads were hot tanked at machine shop. Only chsnges were;
comp cams rv cam and lifters
1981 corvette aluminum intake which dimensionally matched the 305 cast iron intake and accepts the rochester spread bore e4me carb.
scratching head.
radiator was purchased from rocksuto and matched original and installed no problem.
I really doubt air/fuel mixture is the issue here. It is most likely an air pocket or a bad thermostat. Pull the guts out of an old thermostat and use just the body as a restrictor. Install it and see if the issue goes away or persists. I run lean cruise at 17:1 air/fuel ratio and have not had overheating issues. There is actually less heat running leaner because there is less fuel to combust. Any chance your balancer/timing pointer is off. Retarded ignition timing can add a good bit of heat.
Hello,
I had rebuilt the motor and installed new Comp Cams RV cam and lifters. The timing cover was rusty and mark was not legible so I installed new identical timing cover (dorman repro). The Harmonic Balance was original (oil soaked and rubber was cracked) so I bought new replacemrnt.
New Cover and HB were confirmed visually to be identical to old (location of pointer on cover, keyway and timing mark on HB).
I accurately degreed the cam to confirm the cam specs using moroso wheel and a dial gauge on number one piston so I know my timing marks are spot on the #1 TDC. I just reconfirmed the distributor install vs #1 TDC as my mechanic brother was on my case to make sure that tne distributor was installed correct.
The car idles pretty well at idle. Motor seems to prefer 10 degrees BTDC vs 6 degrees BTDC.with 4 pin disconnected. The car will not run with the Hood Sticker spec of 0 degrees BTDC with the 4 pin disconnected.
On a cold start, the car starts right up with no issue. Choke setting is good. I had rebuilt carb 9 months ago before teardown knowing I needed good carb to perform the cam breakin..
As for the TStat, we replaced 1st Tstat that was a 195 degree Gates which had a rubber seat, for a second NAPA Balkan all metal seat. Both were checked in the kitchen in a pan of hot water when we did the swap of the 1st to 2nd tstat. Both opened at 195 degrees (verified by digital thermometer) but I was suspicious that the the 1st Tstat with rubber seat may have been hanging up.
We are sure the Tstat is opening. I can certainly gut the gates Tstat and swap it in, I just think the Tstat is not the issue as we know it is opening and we are running for about 5 minutes on the road before the temperature starts to take off and not subside. As previously stated, we jumpered the electric fan to run 100% of the time so the Fan Temp Switch is not being used./counted on.
Very frustrating as I am out of ideas.
Could the the Distributor 7 pin ICM be defective? It is a` new AC Delco installed with the thermo paste. Could this cause intermittent timing problem while driving, leading to overheat?
Hello, Ill answer for my dad lol. She was good for about 8 minutes, heavy load, setting the rings. 3rd gear 4k to 4.5k and coast down to 3k. I never saw the temp gauge go above 220. Then after cruising at 50mph in 4th gear. Like 2300 rpm IIRC the temp gauge started shooting up. this was on the way to the station about 2 miles from the house It would climb up to the red and never start to go down. We installed all plastic ferrings and air dams. After getting gas the car wouldn't start easily, brand new battery, then it fired and we didn't romp on it, but stayed cruising at 50ish in 4th. Seemed decently happy and pretty much stayed out of the red till we got on our street. I'm imagining the starter is getting heat soaked but I'm not sure. We have the cast iron headers on the block right now, but we have a set of hooker mid length headers and a brand new y pipe. but that would probably be after we sort this overheat, unless it might help with the it too. we could also exhaust wrap em up. I've been told headers add heat though.
The fan is jumpered 100% of the time, but its a single fan probably 15inch diameter and really doesn't seem to move all that much air. Radiator was very hot in all spots. Upper hose was hot and lower hose was hot. Heater core hose was hot and hardish too. We tapped on the Temp stat housing with the back of a screwdriver (aluminum intake) and it didn't seem to change any coolant levels or make a noise or nothing.
I don't think the car is running lean lean (but without a wideband 02 its hard to say), No error code from the O2 Sensor, and we will check the voltage out of it as well, but the dwell was spot on, and it doesn't lug through any rpm band. Water/Coolant seems to flow pretty well too. so I'm really not convinced its a lack of flow.
My biggest concern right now is we have the A/C condenser in front of the radiator too, but its currently empty. Would possibly filling the system and or removing the condenser have an effect on cooling for the radiator. Its been circa 30 degrees f out at our house, and the radiator doesn't seem to ever want to come down from 200+ degrees. No fins are bent and it was brand new, and it seems to circulate coolant no problem. I'm not sure if the elec fan is doing enough, or if the ac condenser might be blocking some BTU's from escaping the radiator.
with the EST disconnected it's not going to want to idle well at 6 degrees advanced (or zero).
the ECM should energize the throttle kicker under these conditions to try to keep the idle up
I'd bump the timing down some and try again, even if you just crank it a little retarded by hand without the timing gun on it.
If it's really at 10 base timing (sounds like you've done what you can to accurately measure it) that's too much.
the motor will have problems with this advance especially at cruise when the ECM commands more timing to burn a leaner mixture at low load.
So we're sitting at 6 degrees right now, 10 degrees was when we were breaking in the cam. the car didn't really run to well until we got up to the 4 degrees area. we could kick it down a bit now too. you think octane boost would help with the temp too? I mean it's only a stock block so I don't even think it's 9.5 to 1, but anything to help at this point lol.
normally I would bump the timing up until I get some light ping at throttle tip in during cruise while full hot, with the fuel I normally run, THEN back it off a few degrees.
that's about the best way (IMO) to tune the timing around the stock timing curve and base setting.
6 degrees base may cause some pinging (or maybe not with higher octane fuel) but is otherwise 'close enough'.
It may, or may not, have been mentioned above but DO NOT rely on the dash guage as an accurate indicator of the actual state of nature at the sensor. It is notoriously inaccurate.
If it's not boiling over now, it's not over heating. That said, you should be able to let it idle in your driveway on a hot day, with the rad fan connected to operate correctly and the fan should come on as temps rise then shut off as they cool...until the car runs out of gas. an ifrared temp gun can read the temp at the water neck, should be near the t-stat setting.
If air can get through your condenser you should be fine. Sometime leaves and crap get between the condenser and radiator but you would have likely noted that when swapping the radiator. If air flow through condenser is questionable for any reason (**** ton of fins bent, etc.) and it's empty of refrigerant, take it out and try. it's only two line fittings and four 10 mm self tapping screws.
If your dwell is responding correctly you're as good as the ECM is going to get as far as rich/lean, although always remember it's only reading one bank. Since your plugs all look the same you're likely good on both.
Today when we both got home from work, my son pulled number 1 Plug and it was white/ash grey after our run last night. So we are very lean.
I had purchased a new Bosch O2 sensor last year but when I had installed, I seem to recall there was a problem so I had reused the original.
We never got an O2 Sensor code before rebuild or now, so I assumed we were good with original o2 sensor
My son suggested we change the O2 sensor as car had 100K on it and car was sitting for three years. We started up after switch and took out for a run. We drove a good long distance, climbed a long 40 degree grade by our house (we live in a hilly town) that is about a qtr mile long. Temp on gauge sitting between 200 and 220 for a good long time. We then headed down hill and headed into town. Drove about 3 or 4 miles at speeds up top 50 on country roads. Everything looked good so we turned around and returned. Heading back we got stuck at a light in town and temp started to creep. It went over 240. Then we started moving, but at that point the temp climbed into the red and stayed there, We drove 2.5 miles from the light to our driveway, We pulled in and popped hood. When it started to overheat, car had already been running at 220 on the gauge for about 10 minutes and about 6 to 8 miles.
We observed that the radiator cap had lifted and there was coolant around the radiator fill area but it was not bubbling out of the overflow but over flow was swelled to top but no coolant was exiting the vent cap and the bottle was not bubbling. There was a rumble in the upper hose.
We shut it down and went inside. Went out twenty minutes later to pull car in the garage. It started up after a short crank without difficulty but when son shut it off after running 30 seconds, it dieseled for a few seconds.
We feel the O2 sensor made a big difference. I plan to pull number one plug when cool to compare to what we saw before this last run.
We also plan to take the timing back to the 0 deg BTC spec and see if the motor will run and how it runs.
I am now concerned the radiator cap, which is new, may not be hold 16 psi. Why is it leaking around the neck when it should bubble into the bottle?
We are leaving the new O2 sensor in.
Car has not thrown any SES lights yet.
Electric fan still jumpered to 100% on and we had good heat from dash vents
We have a gen 4 camaro double fan we can put on. Have to see how to wire two fans as the Gen 3 only has one fan.
radiator and condenser are new/clean and nothing in between. Condenser not yet hooked up as we did not put the new AC components or hoses in yet. We just in stalled a new Condenser which is capped off and a new evaporator which both are capped off by the manufacturer to preserve clealiness. Plan is to restore the AC this spring after we get everything else debugged (like the overheat problem !)
If it heats up driving over 45 mph, you have issues outside of the fan operation. Air flow cools the engine above 45. Both my 84 and 95 will drive down the interstate with little movement on the gauge, stays right at thermostat temp. Lower speeds and idling, temp move up and down with fan operation.
If it heats up driving over 45 mph, you have issues outside of the fan operation. Air flow cools the engine above 45. Both my 84 and 95 will drive down the interstate with little movement on the gauge, stays right at thermostat temp. Lower speeds and idling, temp move up and down with fan operation.
I was thinking the same thing, but the temp stayed consistent 220 and under while cruising at 50. only after pulling a u turn and idling for about 30 seconds did the gauge start to creep past 220. from there it was only a 35mph section till the light, about 1 mile. so it climbed up slowly until we idled at the light for 2 minutes. it touched the red, and just kinda stayed there and dropped a hair as we started going 50ish again home. it was about 35 f out, so I'm not sure if once you get up to red on dummy dial it just kinda sticks there until it really cools off, but after about 3 minutes of not running the temp gauge was back to 3/4 and really didn't hesitate on the starter so it didn't seem as hot as previous runs, and this one lasted about 3 or 4 times as long. outside of a thermal gun with the hood open is there a better way to get temp readouts especially while driving or is the dummy dial good enough for government work?
It seemed to run a hell of a lot better with the new O2, so we'll set timing again and check dwell, and possibly look at doing a lt1 dual fan swap, will need to cut up the upper rad plastic support to do it though. The car is a single electric right now, and the part numbers for a 95 fan motor spec out to the same as the one on the car.... but now there's 2 of em instead of 1. so we'll need another 30A relay or the likes to get both to spin, but even the shroud seems less "cheesy" then the og LG4 fan. and connectors are all the same, so it shouldn't be toooo hard to do. crossing my fingers on that one though. The sticky board on cooling didn't talk to much about retrofitting an lt1/LS1 shroud on a single fan though, and internet search didn't yield that good either, so aside from wiring I'm flying a little blind on the mounting of it.
I suspect that you have a whole lot of air leakage around the radiator core.
What are you using for a shroud, and does it completely enclose the rad core?
Or is it just a fan attached to the radiator?
Go to HD or Lowes and get some foam insulation to seal the radiator all the way around the core support.
Premium Fel Pro that came in the Engine Rebuild Kit.
We did not put the heat rise block offs in so gas passes under the carb..
We removed the passenger side heat riser valve as it was corroded in place and our plan is to swap over to hooker headers when we get this overheat debugged.
a failing O2 sensor will normally result in a richer mixture, which is a good thing because richer is less dangerous than leaner
certainly won't hurt to swap the O2 though.
the dash gauge is NOT even good enough for government work, although as a federal employee in facilities maintenance and construction, I may be biased.
the dash temp guage will not provide a linear response (hence the non-linear markings on the dial face). consider it to be a wavy pointy thing that moves at random times due to unknown forces...sometimes in correlation to the water temp.
a mechanical temp guage can be bought fairly inexpensively and temporarily installed in the engine bay or run to somewhere in the cockpit. I'd find an alternate method of measuring the actual temp before getting too worked up. You don't say it's boiling over and you may be shutting it down just before it does.
OK, As follow-up to my post #36, I pulled number 1 spark plug today at lunch time (working from home) and it was very white/ash grey. Maybe even worse than yesterday so this car is running very lean.
I threw up my hands and called COMP CAMS. Gave them the part number for the cam and lifter kit, the motor details (305 Vin H Carbureted with CCC Rochester) and told him about the recurring overheating.
Tech guys immediate answer was that this CAM cannot be used with CCC Carburetor or fuel injection. He stated that the cam improves the volumetric efficiency of the engine from stock, increasing the air flow and thereby needing more fuel. He stated that the CCC carburetor cannot be "tuned" to meet the fuel needs. He also said the fuel injected motor would not like it either without a remap of the fuel/air.
I challenged him to test his commitment to this statement and he was resolute that we need a different carb to meet the fuel demand.
So the good news is I have a Rochester from a 1979 K10 350 SBC and a Vacuum advance distributor that should be richer.
It is cold as hell in NJ next few days so my plan is to clean and rebuild this carb. I have to see if I can switch it over to electric choke since it currently has a thermostatic choke. I also plan to refurb/clean the vacuum advance HEI distributor.
I will install both and see what happens before I report back. Should be a few days but I will let everyone know how it results. Hopefully sucessfully.
More to follow. Thanks all for the help and advice so far.
As an FYI, the Cam and Lifter Kit I installed from COMP Cams is as follows:
that's the old XE 256 H comp cams. I've put well over 50,000 miles on one under a ccc-qjet back in the day. it was a little rough at idle but was otherwise a good motor with decent (+20 mpg) mileage. always ran cool.
Many others have posted good experience with that cam. Never the less.
JUST TO SEE:
try running it with the CTS connector disconnected. this will confuse the ECM into thinking the motor is cold and run it in enrichment mode.
you can also run it some with the MCS disconnected. this will run it full rich (meters out of the jets) so be aware it may gook up your plugs after a while.
If the dwell is responding to O2 readings, varying dwell at idle +/- 5 degrees or so; and responds to a rag over the throttle bore then the mixture is probably pretty good. At least the ECM thinks so.
there was a member once who had a lean motor where the dwell was otherwise good. chased a bunch of stuff around until he found a vacuum leak somewhere. the dwell didn't respond to the leak as expected. he found it and all turned out rosy. I'll have to look that up.
by all means try a mechanical carb and a mechanical dizzy and see how it does IF you can do so without too much $
NAF, you are correct that it is the XE256H-10 Cam.
I had already changed every inch of vacuum line on this motor and every line is brand new with spring clamps.
I have carefully put everything back together.
I retained the evap canister system to vent for the fuel tank and purchased a new thermo vac switch (TVS) that screws into the manifold and purchased a new three way Rochester cannister control valve that ports the vacuum and lets the carb suck the evap can until the motor warms up to burn off the condensed fuel vapor.
If it is a vacuum leak, I would be surprised, but I should be able to cap off every vac connection on the carb and that should address that potential.
The carb itself was torqued to spec to the intake manifold with a brand new 1/4" fiber gasket.
It is very cold today so I do not plan to mess with it. Tomorrow/Sunday look more likely.
I am not getting any SES lights.
The vac connections I have on the car are:
1. Power Brake Booster Hard Metal Line and brakes are working fine
2. Vacuum Pressure Sensor which comes of back of the car (Port N)
3. Vacuum Secondary Dashpot which share connection with the Stove pipe damper on the Air Cleaner (Port B)
4. The PCV Valve (Port L) the AIR system was removed by me before rebuild. The EFE TVS was deleted and plugged on the Tstat neck.
5. Port J (EGR) is capped off as EGR was deleted before rebuild
6. Ports H is connected to the Purge TVS Switch on Manifold
7. Ports K & T are connected to the cannister control valve.
Not sure what vacuum leaks there could be, but I can certainly cap off:
Port N
Port B
Port K
Port T
Port H
And then I can plug the vacuum connection that goes to the HVAC vacuum reservoir near the wiper motor but I will lose control of the Register Dampers under the dash.
I can also add that all the vacuum system was rebuilt by me and the EGR, Heat Riser and AIR systems were deleted by me and the car was run before we disassembled. I wanted to get everything right before we rebuilt motor and I new I needed a reliable carb and distributor to break in the cam.
OK, As follow-up to my post #36, I pulled number 1 spark plug today at lunch time (working from home) and it was very white/ash grey. Maybe even worse than yesterday so this car is running very lean.
I threw up my hands and called COMP CAMS. Gave them the part number for the cam and lifter kit, the motor details (305 Vin H Carbureted with CCC Rochester) and told him about the recurring overheating.
Tech guys immediate answer was that this CAM cannot be used with CCC Carburetor or fuel injection. He stated that the cam improves the volumetric efficiency of the engine from stock, increasing the air flow and thereby needing more fuel. He stated that the CCC carburetor cannot be "tuned" to meet the fuel needs. He also said the fuel injected motor would not like it either without a remap of the fuel/air.
I challenged him to test his commitment to this statement and he was resolute that we need a different carb to meet the fuel demand.
So the good news is I have a Rochester from a 1979 K10 350 SBC and a Vacuum advance distributor that should be richer.
It is cold as hell in NJ next few days so my plan is to clean and rebuild this carb. I have to see if I can switch it over to electric choke since it currently has a thermostatic choke. I also plan to refurb/clean the vacuum advance HEI distributor.
I will install both and see what happens before I report back. Should be a few days but I will let everyone know how it results. Hopefully sucessfully.
More to follow. Thanks all for the help and advice so far.
As an FYI, the Cam and Lifter Kit I installed from COMP Cams is as follows:
CL 12-234-2
Best regards
Comp Cam guy is clueless, TBH. That cam will run in a 305 and you can also put more cubes under a CCC Q-Jet with minimal changes. I put a 403 Olds with early 70s 350 heads and a cam more aggressive than you have in that 305 under the 307 computer carb in my Cadillac Fleetwood. Its relatively simple to jet up the primaries if it even needs more fuel. That being said if you are just cruising around it is totally normal for the plugs to look white and ashy. Dark, sooty plugs indicate the engine is too rich. As I also mentioned if it was too lean you would know about it from drivability issues, bucking, pinging, bogging, etc. Less heat gets pumped into the cooling system with the engine running lean. The mixture control system is fairly dumb compared to EFI. Yes the VE changes with a camshaft, however the ECM is only altering the duty cycle of the mixture control solenoid in regard to oxygen sensor feedback. After about 50% throttle, the mixture control solenoid is shut off by the computer and the power tip of the metering rods is extracted from the jets. The metering rods have steps. A rich and a lean step. If the oxygen sensor is reading rich, the duty cycle increases and the fat end of the tips stay in the jet more. If the oxygen sensor is reading lean, the duty cycle decreases and the thin end of the tip stays in the jet more. You can change the jet to a larger jet. Going to a non computer carb is going to cause you other head aches.
These plugs came out of a 500 hp small block with EFI. Notice after miles of cruising around, not at WOT they are white and ashy too. Plug reading is largely irrelevant unless you stomp on it up to speed, put it in neutral, shut it off, then immediately pull the plugs.
Our plugs look more white/ashy grey than the ones in your pic
Nothing is happening here until it warms up. I started looking at ordering rebuild kit for this other carb but I have got stuck on the choke. I choke is different from the IROC(thermostatic spring/arm bolts to manifold vs electric on ITROC ). I can't really figure it out because the motor I am taking it off of is from a 79 chevy truck and that manifold has the boss casting to receive the choke arm and the fuel connection is 90 degrees like all Chevys, but the rochester number says it is a 1977 to 1979 B-O-P and I can only find that the 403 OLDs rebuild kits for a 1978 Trans Am match this Rochester Number. No chevy rebuild kit has this number in its series. Very strange. If I understand the Date Code, the CARB was manufactured in 1983????
I hear what everyone is saying about this cam should work but like I said, I challenged this comp cam guy and he was firm on his position. I am an engineer for a living and buy technical equipment and asked him every question I could and he responded with technical explanations why I am running lean and why I can't solve it with the CCC carb.
I repeat his explanation as follows: The VE of the motor has increased so we have more air and need more fuel than the CCC and its computer are setup to deliver, and at the same time, the vacuum is slightly decreased with this cam which further impairs the CCC Rochester to deliver the fuel it is tuned/programmed to deliver (which again he says is aleady not enough for the higher VE). It makes sense to me but I appreciate everyone's true world experience that says that it works because you have done it even when the engineers say it can't (believe me, being an engineer, I have been there before). The Bumble Bee flies even though by calculation he cannot.
COMP CAMS position is this cam does not work with the GM CCC carb and that I need to change the carb to mechanical type.
So, therefore, we are lost and I have lost hope. The only other thing that we have changed about this car is the intake manifold. We switched the cast iron manifold for an 1979 aluminum corvette intake that was an exact bolt up including all the bosses for accessories etc. My friend hooked me up with it. It was visually compared to all features of the cast iron manifold that came on the car and was determined to be identical by me, but much lighter. The only detail this intake has that is different is it has the port for a hot air choke but we blanked that off with a cover plate and RTV (just like EGR port) as we are using electric choke which is stock for this 1986 IROC.
We know the cast iron intake that came on the car was not original because it was OEM chevy red (not repainted, it looked original paint but from another motor) and the rest of the motor was corporate black and rusty. We cannot ask why it was changed because prior owner is deceased.. Manifold was sloppy install with gobs of white RTV.. When was the last year Chevy used corporate red? I know they were red, then blue than black.
1976 was red, 1979 was blue and at some point GM made the SBC V8s black.
Also when I disassembled motor, the timing chain and gear were original. It was the GM nylon sprocket which had cracks in the nylon and was ready to be changed at the 98,000 miles the motor showed on the odometer. So manifold was changed but no cam swap as Timing Chain/Gear was original. Why would they have changed the manifold on this motor? Or changed the cam without doing a chain? Many questions, no answers.
I am all ears if someone has suggestions what can be done to address the overheat, or at least advise a test to confirm the carb/distributor will work (or will not work).
We are stuck in the driveway until this is figured out.
And so far, the temps have been mild/cold in NJ. This will not be a summer driver like this.
the comp cams tech guy is right, taking into account his priorities and assumptions of your expectations and ability
that cam probably won't idle as well under the ccc-qjet as it could under a manual carb or more tunable EFI.
will it work? I generally liked it, although I daily drove it for a few years and sometimes got tired of the idle. averaged over 20 mpg. it's still in a box in the garage but the lifters got lost so it's probably trash
I had it under a 350 with vortec heads and headers. full accessories including A/C. automatic trans. (now that car has a roller LT4 hot cam, fitech and a T56-,,I daily a BMW with the N52 now, times are going to make me go turbo but I'm holding out)
when you get time, see what the actual temps are, maybe you're not as bad as you think. I'm a civil guy though, and a guess is sometimes a perfectly acceptable engineering solution for us.,,,,,,
My first suggestions is to get Cliff Ruggles Q-Jet book and learn what everything in the carb actually does if you are not already familiar to the smallest detail with the carb. If you are sticking with a Q-Jet you need to know what the various passageways and restrictions are for. Any emissions Q-Jet will give better results with the fuel curve richened up and that requires a pin vise with sequential numbered precision drills, and some know how. Aside from the mixture control solenoid being used at idle/part throttle the E4ME Q-Jet functions much like any other Q-Jet.. If it were programming, unplugging the mixture control solenoid puts it into full rich mode. From memory the base timing on a CCC Q-Jet SBC is 6* BTDC, 10-12* would not be unreasonable with a cam change. The timing values programmed into the ECM are fairly low in both advance curve and amount. I made double the HP and had nearly 100 cubic inches more under the 307 CCC Carb and loved the way it drove. I eventually converted that car to GM TBI because it was far simpler.
I still think it is completely the cooling system. By self-admission you have stated that the fan is not pulling much air. You also have stated that it is wired to run 100% of the time. The fan could actually be blocking natural air flow going down the road. Also the most overlooked part is often the valance air scoop on the bottom of the radiator. If it is damaged or missing, overheating is almost a certainty on these cars. The stock size radiator core should not have an issue cooling a 350 much less a 305 if it is getting adequate airflow. My old G20 van used basically the same radiator core as these cars and towing a trailer uphill at or near sustained WOT it cooled just fine thanks to a massive mechanical clutch fan drawing in air at all times. It is completely possible that airflow is stagnant across the radiator even at 45-50 mph.
The weirdest overheat I even tracked down was actually a cooling fan that was blowing into the radiator rather than pulling through it. 5.0L Mustang would run cool at idle, cool at 75-80 mph, but overheat if driven 35-50 mph. If you are missing air dams, air guides, etc not amount of mechanical swapping the fuel/ignition system is going to keep it cool.
The best cooling system on these cars is one that is nearly impossible to duplicate now. The early cars had an actual fan shroud and a mechanical clutch fan that moved a lot more air than the electric fan setups that came after. The clutch fan setup I had always kept the temperature gauge under 1/2.
So Im on my dads account right now. (Im That86IROCZ btw). So I dragged him out to do some basic stuff today as its been 10 degrees out give or take.
I went out and checked #1 Spark Plug. It was decently ashy, so i cleaned it up a bit and stuck it back in.
Then we hooked up a test probe to the O2 Sensor. After being in closed loop, and warming up for 20 minutes or so, temps were 220, no boiling. at 800 rpm idle the sensor would bounce from .05V to .65V, and it would fluctuate about 3 times a second. Then at 2k rpm, It was holding .55V but fluctuating between .35V and .75V, didnt drop to 0v too often, much less than at idle but it still seemed a little jumpy. Brand new Bosch O2 Sensor btw. Didnt ground it out and goober it either.
Then we set Timing to 0 Deg BTDC at 700rpm factory spec. The cam is adv 4 degrees and the motor seemed happy. But it seems happy at pretty much any timing from 0-4 with the 4pin disconnected.
So now we decided to plug all vacuums except necessary stuff so no more carbon evap canistor, and we plugged some other bs. We found the Vacuum box above the brake filler to have a loose ish connection, we cut the line back a bit and put on the 4th gen vacuum box from a 95 Formula. Same dimensions and all, but it fit snugger on the nipple. Car idled muchhhh smoother and seemed decent. We took it for a quick drive, and it seemed solid. Still overheated after 15 minutes or so, but it seemed happy. We have to reset the curb idle as it wouldnt kick down from mid idle, so it was 1800 for that drive. but we barely idled. It didnt boil over after the run. and it fired right up when we adjusted the idle again. This was about 10 minutes ago, just waiting for the car to cool again to see what idle will be like.
The only weird part on the drive was this. So we have a big half mile hill like 35 deg incline. So we climbed it starting at like 220 on the dial. At the top it got up to around 240, then it took off once we climbed it, went all the way up to red. We pulled a u turn and started heading down the hill. We basically engine braked down the hill and the car cooled all the way down to 220. It went from red 260ish to 220 just by keeping it in 3rd and not touching the gas. It just plummeted while engine braking, like ive never seen. Then pulling in the house it slowly crept up, but shut it off in the driveway. A little bit of gurgling in the upper hose, and the overflow coolant was a little bit higher than full hot.
Im gonna go pull the plug after the run, and hopefully it isnt ashy, before the run it was shiny new with scotch brite, and drop a pic in the chat.
Thanks for all the support and hope we start getting some better results.
I’ve installed and tuned bigger cams than that one in the L69s and LG4s with the computer quad. However your cam is starting to get on the borderline of needing more than just idle mixture screws and air bleed valve adjustments. Below are the adjustment points in relative order of “need”. Even the smallest of performance cams will typically need idle mixture and air bleed valve adjustments. Bigger cams, maybe even yours, could require a throttle position sensor adjustment (because you may have moved it out of range when raising the idle speed with the adjustment screw). The bigger cams (bigger than yours) will almost always require adjustments to the lean and rich stops to run right. NAPA used to carry the idle mixture adjustment tool and the air bleed valve adjusts with a flat screwdriver.
I’ve installed over 14 different cams in L69s and LG4s back in the day and tuned a lot more computer carbs than that. That’s probably a decade before the guy you talked to at Comp was born. So, don't let that guy discourage you - your cam will most definitely work with the computer carb, assuming you “tune” for it (at least the idle mixture screws and idle air bleed valve).
I haven't seen the book Fast recommended, but this is the same book I bought back then and recommend it to those starting out. The secondaries of the computer quad works just like the non-computer version, so all the information about secondary tuning applies to the computer carb. eBay has one that looks to be in decent shape for a decent price.
ALL the smog era Q-Jets will be calibrated lean from GM and all of them will need adjustments.
Idle Mixture screws. Stock setting is 3-3/4 out and I generally go 5 after resizing the idle down tubes, idle channel restrictions and idle mixture screw openings. Some setups need as much as 6-7 turns out on the idle screws. With those metric idle screws, factory ICR and idle down tube sizing, I have seen some non computer engines like the L82 factory set as much as 7.5 turns out to get enough fuel to idle. I would open up the idle and off idle transition slot fueling a bit because you can always lean it back out as needed with the idle air bleed screw on top. You can take away fuel by adding bleed air, but its really tough to add it the same way.
Bypass air. Once you start having to really open the throttle plates with the idle speed screw, the carb needs more bypass air. You are going to have the same issue with a mechanical version as well. Bypass air allows the carb to properly meter fuel off-idle without having to crank up the idle speed screw. You can actually get so much velocity on the venturis that fuel starts to pull through the main metering circuit at idle aka nozzle drip. Bypass air is air drawn through voids in the casting and metered by orfices drilled into the base plate. It allows air to bypass the primaries without being drawn through the venturies and boosters. Typically need to go from 0.060-0.080 up to 0.95-.110 on the bypass air for a cam that size.
Accelerator pump, get performance one with a longer stem and stiffer spring. Then drill the discharge holes 0.030-0.032" makes sure you use a new check ball after using the old one to burnish the seat. Fuel needs to discharge from the accelerator pump instantly when the throttle is moved.
Timing...The 85 TPI 305 I converted to carb which for all practical purposes makes it a L69 liked 35* total advance at WOT. The LG4 computer I located the spark tables in only commands about 26-28* of timing at WOT and only in the mid 30s at cruising speeds with the initial set at 6*. With a modest cam I think it will be happiest in the 10-14* initial range. Set it at 12*, shut it off, reconnect the EST, remove the negative cable to clear out the codes, then refire it. Bring it up to ~3500 rpm no load and check total advance. My guess is it will be in the low to mid 40s which is where it needs to be.
Also something that gets messed up often, when adjusting the mixture feedback, make certain you use the 6 cylinder dwell meter. 30* is in the middle, but I tend to error on slightly higher. Higher value means the base calibration is richer overall and there will be more fuel available when the carb enters open loop for acceleration enrichment.
If you think it is lean fueling causing the overheat, unplug the mixture control solenoid and drive it around a bit. The carb will default to full rich when the solenoid is unplugged.
01-28-2023, 08:27 AM
