Lauper84

Hey everyone,

I’ve read a million posts and tried every solution I could find, so needless to say I’ve got a tricky one for you—the car dies if I set the idle lower than around 850-900rpm in park. The car dies when shifting into gear if sitting idle is lower than 1200rpm.

specs: 84 camaro mostly stock 350 engine out of an older camaro, but with headers, new 625cfm Holley street demon, new billet distributor/cap/rotor, new intellitronix multispark ignition, and lastly brand new lunati bootlegger cam ( Advertised Duration (Int/Exh): 269/296 ;Duration @ .050 (Int/Exh): 224/236 ;Gross Valve Lift (Int/Exh): .485/.485 ;LSA/ICL: 108/104 ;Valve Lash (Int/Exh): Hyd/Hyd ;RPM Range: 2600-5800) lifters, and quiet timing drive. 700r4 transmission with likely stock stall. Running 93 octane. 9:1 compression

Tuning details: timing recently advanced to ~18 degrees at 1000rpm because it was running sluggish with less or more. Roughly 16hg vacuum at 1000rpm. Carb screws set to the point where it stops idling up.

*NOTE* car had the exact same problem before all the new parts listed above.
*NOTE* depressing brake with booster vacuum connected does increase idle ~100rpm—See below for more detail

What I’ve tried so far with little to no result: changed plugs and wires, advanced timing, tried plugging all vacuum ports including brake booster one by one and all together, located all vacuum leaks and sealed, rechecked for additional vacuum leaks (and found none), and tuned carb excessively.

I would be totally satisfied to get it to idle down to about 900 in neutral and 700 in gear but nothing is working! I’m perplexed!

GeneralDisorder

iTrader: (1)

You may need to add a fast idle solenoid to bump the idle when it goes into gear.

GD

Lauper84

Never thought about using one for anything but AC bog down but that’s not such a bad idea to try. Hopefully there’s something free-ish I can try first though. Lol

LiquidBlue

was curious what vac should be, ran across this

http://www.gregsengine.com/using-a-vacuum-gauge.html

sofakingdom

iTrader: (1)

A vacuum gauge will tell you what the vacuum IS, but not what it SHOULD BE.

At a guess, with that cam, the vac SHOULD BE around 13 - 14" at 750 - 800 RPM. It should have NO PROBLEM idling at that speed.

I've never used one of those carbs, but I have a hard time believing it can't deal with that little of a cam.

Sounds like either a mechanical or a carb (fueling) problem to me. How are the valves adjusted? What's the fuel level in the carb?

dan5

What kind of ignition coil are you using and can you substitute a different one? That ignition system is likely driving it hard. I've had coils that would give a weak spark. They would run off-idle fairly well, but couldn't handle idle speed and would stall.

Lauper84

very helpful article. I’ll dive further into this soon.

on vacation at Lake Superior right now but I’ll check and get back to you on these questions when I get back home.

you know, I didn’t even think about it but I’m running some off-brand probably chinese “high output 65k” coil. It could be the weak link. Any coil recommendations?

sofakingdom

iTrader: (1)

Problem is probably not the coil.

Note that I am NOT saying "your coil is good"; NOT saying "don't check your coil"; NOT saying "a coil can't make a car run bad"; NOT NOT NOT NOT NOT.

Only, that the problem you describe is PROBABLY not the coil. Typically when coils have trouble, it happens under high load, when there's lots of material in the combustion chamber, and it makes a better insulator, thereby needing more ooomph in the spark to enable it to jump the gap. Idling is the easiest operating condition for a coil. Therefore a failed or weeeeek or crappy coil, while CERTAINLY a possibility especially when it's some one of those "too cheeeeep to be as good as it claims" POS chinesium things of that sort is involved, is MOST LIKELY not why your car has this problem.

Your problem is typical of going suddenly lean when the RPMs drop; which is of course when the main system (venturis, jets, etc.) which works off of AIR FLOW, STOPS feeding fuel; and the idle system, which works off of VACUUM, is supposed to be left to take over. For whyever, the symptom you describe is that of a carb's idle system not working. Which isn't always the fault of the carb itself, but of course, can be.

Also you mention "had the exact same problem before all the new parts listed above"... what about with a different carb? Did it have this before THAT carb was put on it? Has this motor EVER run right?

GeneralDisorder

iTrader: (1)

Yeah I also thought about a clogged or improperly operating idle circuit..... but he says it's a new carb.

Still - it does sound like the idle circuit is not delivering fuel and you are trying idle on the mains.

GD

Lauper84

Yep that’s why this one seems a little extra tricky. I acquired the car around a year and a half ago—the carb that came with it, parts store edelbrock 650, had the very same problem, so I replaced it with a brand new street demon 625 (and at the same time replaced the distributor and added electronic ignition), same problem. Identified vacuum leaks, sealed them and at the same time replaced the cam, lifters, and timing set, broke it in, same problem. if I can get ahold of a different carb temporarily I might try that before pulling this one apart but I’m still feeling stumped.

Lauper84

I'm about to get some new aluminum heads, so I'm guessing that will exacerbate the lean condition at idle.

dan5

I understand your comment and reasoning. You are probably correct. I know this is a Camaro board, but physics doesn't care about brands. I can tell you that my 428CJ Mustang had very nearly this exact problem when it was up to operating temp. It would run fine if I left it up on the fast idle cam. If I let it go down to normal idle stop, it would begin misfiring, and it would stall in just a few seconds. I chased the fuel system from tank, pickup, lines, pump to carb for months. Had the carb apart-cleaned and rebuilt twice (and I'm rather proficient with carbs). No improvement. Then I started checking electrical and spot checking temps underhood. My almost new Accel chrome coil had a repeatable fault when it was above about 160-170 F-checked with an IR thermometer. New coil cured it. Idle is also a demanding point for spark in its own way. If the spark is weak, the plugs can load up quickly and it looks like a fueling problem.

Lauper84

just went ahead and ordered a pertronix coil. Worth a shot.

BIRD91ZRAG

iTrader: (1)

You need a looser torque converter. That cam needs at least 2400 stall in a 350. No amount of tuning will fix it.

Lauper84

Yeah but that wouldn't affect my inability to idle under 900rpm in neutral/park, only my ability to idle in gear without lurching. in fact, even idling in gear at ~900rpm, it only lurches a little. I've only assuming it's the stock tc, I haven't gone under and taken a look yet. The car had a worn down old crane cam when I opened her up among other things, including a shift kit, so it's possible one of the previous owners did work I'm yet unaware of.

Lauper84

New coil didn’t do anything, but I feel better having a reputable brand coil in there now anyway.

After more hours of tuning and retuning and f***ing around with the car, I finally found the culprit. A MASSIVE vacuum leak in the throttle linkage of my brand new street demon carb. I mean you could idle up to 1600 rpm and spraying carb cleaner on the linkage will still kill it almost instantly.

Time to talk to Holley. This makes the second street demon I’ve had bad luck with in my cars. The last one I had to rebuild it almost right out of the box. Wonder why I didn’t learn my lesson then 🤔

sofakingdom

iTrader: (1)

I guess a GIANT vacuum leak is the flip side of A LEAN CONDITION AT IDLE. Sorry I believed you when you said you didn't have any vacuum leaks. Which is what I would have told you your problem was except that I was trying to trust you that you didn't because you insisted so insistently. And except of course that I would have got EVEN MORE backtalk if I'd have told you you did, no matter how much you thought you had "checked".

Don't worry, I'm used to it. Don't waste your time. You can't flame me enough for me to even so much as notice a warm springtime breeze.

Lauper84

lol well I obviously believed you somewhere deep down because I kept spraying around. I mean who could’ve guessed you buy a brand new carburetor and the THROTTLE LINKAGE of all places would be where you find a massive vacuum leak. Holley’s got some ‘splaining to do.

Lauper84

What do you guys think about fuel pressure being part of the cause of this? Pump is putting out 10ish psi at idle, carb likes 6. Ordered a fuel pressure regulator to install while I wait for the carb to come back from repair, but I'm wondering if the fuel pressure could cause a shoddy idle.

sofakingdom

iTrader: (1)

10 psi will COMPLETELY OVERWHELM the needle & seat on most carbs.

Won't cause the specific problem you were having, but sure as hell won't help anything else either. Regulator is the right thing to do. Make sure it's a 3-port - pressure, carb feed, and return. And hook up the return.

dan5

Yes, that pressure is too high and will tend to raise the fuel level in the float bowl or cause flooding if the needle and seat leak. Fuel may drip from the main feed at the booster venturi. Holley usually wants a maximum 7 or 7.5 psi.
What fuel pump are you using? The mechanical ones normally self regulate in a safe range.

Now, back to your carb question. What is Holley doing about your carburetor or what is their response? It would seem very odd to have a large vacuum leak at the throttle shafts. They normally aren't sealed, there is always a small clearance between the shaft and the body. Certainly there is some vacuum / air flow there that will pull in carb cleaner if you spray it there (and you could pull in enough carb cleaner to upset the mixture), but I've seldom encountered gross leaks at the throttle shaft.

Thinking it through, you must not have an excessively lean mixture (usually the case with a vacuum leak) or the engine would just speed up with extra "fuel". The result of the engine slowing and stalling suggests rich mixture. Perhaps you are overdriving the needle and seat and running to the rich side or flooding with high fuel pressure. As someone said earlier in the thread, it sounds as if you are idling on the main circuit. Did the idle mixture screws have any effect when adjusted?

Lauper84

Holley had me send the carb in for flow test and repair; I’ll know more details in a few days. The tech agreed that while spraying some carb cleaner at the throttle shaft should affect running conditions, it shouldn’t be killing the car. Said it might be the baseplate gasket but that it’s a long shot.

Adjusting the mixture screws did affect the idle but not in the amount that I’m used to with other cars I’ve had. Demons actually like a mere 5-6psi. Fuel pump appears to be stock mechanical pump. Ordered a fuel pressure regulator today. If that gets blown out I’ll move onto replacing the pump next.

I’ve had a professional mechanic over for some stuff like the cam swap and he thinks that a 625 street demon is too much carb for this mild 355, but I had one on a 305 a few years ago and it idled better than this.

sofakingdom

iTrader: (1)

That's horse dookie.

Which cheek of his a$$ is he covering?

Lauper84

dan5

A 625 vacuum secondary is certainly not too much for a 355. Even if it was "too big", something like an 850 double pumper with mechanical secondaries, you should still be able to make it idle, it just might not be fun to drive.

Fuel pressure regulator may be a big help. If the idle screws are not as sensitive as normal, you likely are still running on the main system with the throttle plates cracked open too far for effective idle control. If the float level is high and running to the rich side, that would also make it hard to lean out with the mixture screws. The regulator could bring it back into line.

sofakingdom

iTrader: (1)

People get too wrapped up in fuel PRESSURE these days. It's utterly critical for EFI setups; but IRRELEVANT, within certain ranges, for carbed ones.

Carbs work off of fuel VOLUME. They have a fuel bowl that is at atmospheric pressure. ZERO psi. The pump is supposed to keep that FULL. As long as it's FULL, it DOES NOT MATTER what the pressure is. If it can be kept full by .001 psi of fuel pressure UNDER ALL CONDITIONS (idle, cruise, WOT, etc.), then, .001 psi is all it needs. That's somewhat trivial, as far as the #s, since it will always take some amount of pressure to push fuel past the needle valve; but the CONCEPT is what counts. Keep teh fuel bowl full, and when it's full, shut off any further fuel flow into it. Both are equally important. (flow on the one hand, and shutoff capability on the other) If it needs 4, or 7, or 15 psi to keep it full UNDER ALL CONDITIONS (idle, cruise, WOT, etc.), then, THAT'S what it needs.

The operative concept being, the fuel bowl MUST remain FULL at all times; and, the needle & seat, which controls how much fuel passes into it, must retain control of the fuel AT ALL TIMES. "Control" means, when the bowl is full, the needle valve MUST shut off the entry of any more fuel; and when the bowl is less than full, the needle valve must allow fuel in, to fill it back up.

Most carbs will work best with somewhere between about 4 and 6 psi. Your carb has a pretty large needle valve, therefore will work fine at as low as the 4ish end of the scale. Bear in mind, the larger the orifice that lets in fuel (the # of sq in), the harder of a time the needle valve will have cutting it off, since the float will have to exert the # of lbs against however many sq in to be able to resist that many psi (lbs per sq in). This stuff is JUST NOT THAT HARD; even I can understand it. Granted my earlier education was as a rocket scientist, but I don't need 99.999% of that to figure this out.

Apart from all of that, you have to gain control of several apparently competing interests here.
-
-

• 625 CFM is a SMALL carb. The stock GM carb that came on 305s was about 750 CFM. Needless to say, a 305 didn't use "all" of that; but the mere fact that the carb flows some number, DOES NOT NECESSARILY preclude its use on some motor. Butt, a 650 CFM carb is well, widely, and FOR MANY DECADES known to be a good carb size for a typical street 350, and yours is no different.
• Carb CFM is NOT related in any direct way to idling. It's more connected with max power, max RPM, max max max max max stuff. One that's too small will make the motor peter out at a lower RPM than it otherwise might; one that's too large will act like the motor is being hyperventilated.
• Whoever tries to tell you anything, you need to consider THEIR interests as well as yours. How do they get paid? Did they tell you to pick whatever you have? Whose ox gets gored if you decide they're full of excrement? Are they trying to maintain their aura of "expertise"? What are they trying to sell you? and so on. (My advice is FREE: I have no dog in this hunt.)
• Telling you this kind of CRAP without any sort of troubleshooting or measurement or changing something to see what effect it has, is BULL PLOP. "Tuning", as us old farts that have been doing this probably since before your mama was a gleam in your grandma's eye, consists of establishing, best as we can, what the car is doing NOW; making a SINGLE LOGICALLY DIRECTED change to the car based on what the car is doing vs what we want it to do, and MEASURING the effect; then making further changes, in the same direction or in reverse, always looking for improvement. Once all of the "handles" we have to make changes to, cease to make improvements (i.e. it's as good as it gets), we can consider the job done.
• "Tuning" is always done in a SYSTEMATIC LOGICAL RATIONAL ORDERLY fashion. You can't "tune" a defective car or motor. It has to AT LEAST be "working" properly. Putting 10 psi on a carb IS NOT "working properly".

And so on...

FIX your fuel pressure so that it's into a range the carb can successfully work within. Then FIX any other "broken" aspects you know of: throttle cables that don't open all the way, vacuum leaks, ignition problems, etc. etc. etc. etc. You CANNOT "tune" a broken car.

Once the car is FUNCTIONALLY CORRECT, it will become possible to make adjustments to optimize it.

Lauper84

All this info has been really helpful guys. I love the community of knowledge you get with owning a muscle car. My dad was a mechanic and tried to teach me some of this stuff 20 some years ago when I was still a dumb teenager, but, well, I was still a dumb teenager and didn't listen, and then he had a brain aneurysm burst (don't worry, recovered), so he doesn't remember 2/3 of it either! And I gotta say sofakingdom, your posts are always stern, extremely informative, and amusing all at the same time. Actually makes this headache of a situation a little fun again.

Once the carb comes back and the fuel pressure regulator is dialed in, I'll give everyone an update on where everything stands--and hopefully it'll be standing strong.

NoEmissions84TA

iTrader: (1)

I'm glad you found the carb problem, but you still could have a carb base gasket problem if you are using a square-bore carb on a spread-bore intake manifold. Usually you need an adapter plate to help cover the widest part of the manifold's carb mounting flange, otherwise you could/would have a vacuum leak there.

I am concerned about the old worn out Crane cam. The shrapnel from the worn lobe(s) is continually circulating around inside your crankcase if you haven't taken steps to clean it ALL out of there.

Lauper84

It has an edelbrock square bore intake on it. Unsure which exact model off hand; I’ll have to check again.

A good point. We did standard cam break in procedure with Lucas break-in oil when swapping so I’m sure the successive oil/filter changes would’ve helped clear a bit of it out, but what would you advise for helping clear any lingerers?

NoEmissions84TA

iTrader: (1)

I am talking about what happened to the metal shavings from the old Crane cam/lifters?
I you or nobody else actually took the engine apart and completely cleaned that out of there, changed the bearings and oil pump, flushed the oil galleries, etc - then those shavings are still there and WILL cause further damage. Ask me how I know.

A magnetic oil drain plug couldn't hurt.

Lauper84

Should've used a magnetic prefilter when I did the swap. Hindsight is 2020.

NoEmissions84TA

iTrader: (1)

Even if the oil filter could trap all of that debris, it must go through the oil pump's gears first. Keep a close eye on your oil pressure, especially when the oil is hot and thinner.
I won't even tell you what happens to your cylinder walls. There is a slight chance that you might be OK, though.

Lauper84

Okayyy with the carb back from repair and the shiny new fuel pressure regulator dialed into 5 psi, She’s pulling 16hg of vacuum and purring like a kitten at 750 in park/neutral... but still dying when shifting into gear unless I adjust the fast idle to 1300rpm! 😫

Sprayed around everywhere for new/remaining vacuum leaks and all I got for my trouble was a very minor fire from a short in my choke power line. Yaaay.
^^^meaning I located no leaks.

What’s next guys?

aliceempire

iTrader: (14)

going on a stretch, what's it do when you just step on the brake? Vacuum drop? Just guessing a possible booster leak

dan5

Well, now you have it idling in park / neutral and it seems normal. Your description is that it can't handle the load in gear without opening the throttle further. Based on your original post, you indicated a probable stock stall speed and a cam with a power range starting at 2400 rpm. I pulled up Lunati's recommendations and they want a 2500 stall converter (or higher). You may now be in a spot where the torque converter is too tight / too much absorbtion (low stall speed). Just looking at the cam specs, I wouldn't have expected that high a stall requirement, but Lunati should know. To verify stall speed, find a safe location, hold the brakes to keep the car stationary, and go to WOT for no more than 5 seconds-what does the tach read? If you detect any slippage--get off the throttle fast, but the clutches should handle that condition. I used to run that test all the time. If you're way below 2500 RPM, this may contribute to stalling. Then the choice may be either a throttle kicker or a different converter. How does the car drive otherwise? If your converter stall is too low, it ought to be a little sluggish at low engine speeds.

Lauper84

Depressing the brake increases the idle 50-100rpm, so there’s clearly something going on there. Would that really be enough of a condition to cause the resulting shift stall?

dan5

Momentary speed increase as the booster strokes, or continuous? To rule this out (or not), find a safe place where the car is clear in front, set the parking brake and drop in gear without using the regular brake. Stall? Also, if you clamp off the booster hose in park, how much does the vacuum / engine speed change? If you have help, you could do this released and applied in park

NoEmissions84TA

iTrader: (1)

This sounds exactly like the classic problem of too big of a camshaft combined with not enough converter stall and actually idling on the carb's main circuit.
Either SkinnyZ or Fast355 described this perfectly in another thread. Hopefully they chime in.
Let's start here. ECM no longer is in play, correct? Are you using vacuum advance, and how is it connected - manifold or ported?

Lauper84

Continuous speed increase. A few weeks ago I tried plugging the booster off but it didn’t affect the shifting results. I’ll check the vacuum change with clamping off the hose next time I’m out there though just in case.

Yeah ECM gone before I got the car. Using ported vacuum advance. I’ve read about benefits to using full manifold vacuum at idle, but heard that it has a negative vacuum impact at higher speeds.

GeneralDisorder

iTrader: (1)

Having the vacuum advance "ported" only has one single effect. It shuts off the vacuum advance at idle. Once the throttle blade uncovers the port - the vacuum advance is effectively connected to full manifold vacuum from then on - till it returns to idle. It has no "negative impact" at higher speeds because at higher speeds ported vs. manifold are one in the same thing.

For a low manifold vacuum application you should run it to full manifold vacuum - you are going to need the advance due to the slow burn rate (poor efficiency) at idle.

GD

dan5

There can sometimes be benefits to having full manifold vacuum at idle, but it isn't necessarily true that full is better than ported. You need to have the right timing for your engine that is a combination of initial lead, vacuum advance, and mechanical advance. Use of full manifold vacuum at idle with no load tends to cause instability in combustion and increasing misfire and HC / CO emissions. It also increases engine power at light load, that then requires the throttle plate to be closed down and reduce air into the engine to achieve the same idle speed (needs less air to keep running). That is why after about 1968 or so, most engines went to ported spark, it was necessary to meet emerging emissions requirements.
You can try running full vacuum spark at idle and see what happens, but I think that it will likely be negative for you. The reasoning is that you have the car running well with no load and when you put it into gear it doesn't have enough power to pull against the transmission. Currently there is no difference between those conditions with ported spark. Using full manifold vacuum, two things will happen. First, manifold vacuum will be setting spark advance for the 16 inches of vacuum in park, likely near maximum advance. When you transition into gear, vacuum will drop and therefore the advance from the vacuum can will drop, reducing power and making your condition worse. That depends on calibration of your particular distributor vacuum unit. Second, you will need to adjust the throttle plates more closed, reducing air flow and being more dependent on the idle circuit.

If the engine needs more timing at idle, try it with more initial lead to see if it helps. If it does help, then you may need to reduce the mechanical side to keep total timing at WOT where you want it.

Lauper84

Apart from poor fuel economy, what are the potential negatives of just driving the car with a high idle until I can piece together a manual trans swap?

GeneralDisorder

iTrader: (1)

It's still going to have the same problem. It will just turn into a low RPM drive-ability problem when you are trying to release the clutch in stop and go traffic, etc. The torque converter load is just like lightly releasing the clutch to creep the car forward.

Fuel economy isn't going to really be a significant factor with a few hundred more RPM at idle. You don't spend the majority of time there.

Even with speed density fuel injection - my cammed 350 automatic runs 850 RPM idle. It just doesn't like being below 800 and I have a computer that can change the timing in milliseconds for stall saving, etc. That's probably where it's going to live no matter what you do with the transmission. I work with a lot of very experienced tuners are they all said that 850 was a great idle speed for my setup.

GD

Lauper84

Is your set up a manual or auto? If auto, is your idle 850 in gear or just in park/neutral? because 850 is around where I have mine idling in gear now that I have a fuel pressure regulator hooked up.

GeneralDisorder

iTrader: (1)

Mine is a 700R4 automatic with a 3000 converter. Since I have fuel injection my idle is the same 850 in neutral and in gear. The fuel injection adds steps to the idle control valve automatically when I put it in gear. Timing is adjusted automatically to maintain idle speed - it has the authority to move the timing anywhere from 5 to 25 degrees to bring the idle under control and keep it as close to exactly 850 as it can. The closed loop idle air and timing control take care of it without impacting total timing, etc.

GD

Lauper84

Wow. Didn’t know an aftermarket fuel injection system could do all that. Is that the Holley sniper or something else?

GeneralDisorder

iTrader: (1)

Something else. Factory TPI style manifold (FIRST) with factory harness running a LINK standalone with adapter harness.





GD

Lauper84

what a beauty.

Lauper84

Alright here’s an update on what I’m dealing with:

After lots of tuning and the discussions we’ve had on here, I finally resigned myself to idling at 1200 in park and 800 in gear, tried it a bunch of times and it was solid, and honestly I was quite pleased with tuning it down 100 rpm from where it was... so I shut her off and started putting some stuff in the trunk.

Came back, without changing a thing. Fire her up, shift her into gear—dies. Raise the idle to 1300, dies, 1400, dies, 1500, dies. Somehow, in the 5 minutes since I walked away without changing a thing, the problem has exacerbated to worse than ever before, needing a 1600 idle to shift without dying!

I’m at my wits end! What do I try next?

NoEmissions84TA

iTrader: (1)

I LOVE this pic. It speaks to me. It says Screw Pretty - I'M ALL BUSINESS UNDER HERE.