92RS_Ttop

iTrader: (3)

I swapped out my V6 this past winter for a carbed 350 and its giving me some issues with tuning. I've been trying for the 3 weeks now to get it running right and I've made some progress, but its still fighting me. I've searched and tried some of the suggestions I've found and while they have helped some, its still not great. I will freely admit I don't know much about carbs, but that was one of the big reasons I wanted to use one, so I could learn.


When driving the car it has a horrible stumble when I stab the throttle or try to go WOT. The engine almost stalls out and then slowly takes off at first then picks up like it should. when I get on the throttle gently though, it runs great. Changing to a stiffer spring in the secondaries helped this a bit.

Also, it seems to be running a bit rich idling in traffic, but nowhere near as bad as it used to. I especially get a horrible unburned-fuel smell if I sit and rev it. I adjusted the idle mixture screws and the curb idle screw and have this mostly taken care of. The engine idles at about 750 now instead of 1000 and is a little rough but stable. This was done at the same time I changed the secondary spring.

Vacuum at idle is around 14-15". If I rev it hard/normally, vacuum drops to around 5-6. However, when I rev it slower, like when I'm pulling out from a light, it goes up to 20 and doesn't drop till I get higher in RPM's or let off the gas to shift. Just wondering if this is normal as everything I have read about tuning carbs talks about vacuum dropping, not rising?

With it being a vacuum seconday carb, should there be a linkage connecting the primary and secondary throttle levers? I didn't think there should be, but there is one there with a screw and bolt in the secondary throttle lever to limit the travel of the linkage before it starts opening the secondaries.


The engine is a used 2 bolt main 350. I did a basic rebuild on it using the stock dished pistons and some 416 heads with stock size valves. I ported the heads myself, but didn't go overboard on it. Cam is something of an unknown as I picked it up used from a member here. The specs that I have been able to measure are: intake lift .408, exhaust lift .416, lobe separation appears to be about 110 if I eyeballed it right. Duration I don't have any way to measure. The carb is a Holley 4160 model 600CFM vacuum secondary with manual choke. I rebuilt it this winter as well using the Holley Renew kit. Jets should be stock as I haven't changed them, they are 66's I think. Power valve is now a 75 and the secondary spring is the black one currently and it has the orange accelerator pump cam. The squirters give me a good strong pair of streams when I move the throttle lever. Timing is set at 6* at idle with the vacuum unplugged and I used the Mr Gasket advance kit in the distributor with one "heavy" spring and one "medium" spring. I haven't checked total advance as I don't have the balancer marked yet and my timing tab is hard to read.

Sorry bout the long post, I just wanted to make sure I didn't leave anything important out.

Thanks in advance.

92RS_Ttop

iTrader: (3)

I forgot to mention that since I have leaned out the idle mixture and lowered the idle speed, it has been popping and crackling and also sounds like its backfiring whenever I let off the gas and just let it roll in gear. Like going down a hill or downshifting to slow down for a turn. I'm thinking I need to richen the idle mixture back up, but I did that at the same time as changing the secondary spring so I'm not sure that isn't causing the problem as well.

aciddrop2804

Same WOT problem was happening to me with my q-jet. Its bogging down because the secondaries are opening to fast and its getting the air, but not getting the fuel for a few seconds. You need to adjust the secondary spring so that they open slower. I'm not sure how its done on on the holley, but heres an article about it with the q jets that may help

https://www.thirdgen.org/quadrajet

fleetmgr

There should be no connection between primaries and secondaries except the link that drags the secondaries shut when you let off the gas. The nut and bolt is the shadetree method of attempting to imitate the action of a double pumper, and it doesn't work because you don't have the secondary accelerator pump. Remove the nut and bolt, and your stumble should be cured. With this in there, you don't have a vacuum secondary at all, and that's what you need. You get the stumble from the massive quantity of air being presented to the engine before it's ready for it.

Try setting the idle mix this way, and this assumes the float level is correct to begin with:

Open the idle mix screws 5-6 turns
With a handheld tach on the car, turn each screw in slowly. As you turn them in, idle RPM should increase as you get close, and then decrease as you pass optimum. Back them out again just a bit and then close them again, stopping at the highest idle speed. The goal is the highest idle speed with the leanest mix. Assuming your idle speed is somewhere under 1000 at this point, set idle speed last. If in the process of adjusting the mix, the idle speed gets out of line - slow it down and start over.

Do one side at a time.
Don't try to use the tach in the dash.

92RS_Ttop

iTrader: (3)

That's what I figured was happening, and why I went to the heaviest spring. That should keep the secondaries from opening too soon. I'll take a look at the article when I get some time a little later on. Just popped on for a sec to check my thread right now. Thanks for the link!

92RS_Ttop

iTrader: (3)

I was afraid the link was dragging them open too soon. I am assuming it is also the link that pushes them shut when I let off the gas. I'll take the screw and bolt out, although they are set about halfway through the slot and allow quite a bit of travel before the link hits the bolt. I wasn't sure if that was the problem or not.

I will try setting the idle the way you suggested. I haven't heard of that method before.

I have been using an aftermarket tach that I wired in for setting the idle speed. Its nothing fancy, just an old tach I picked up a few years back, but it should be accurate enough still. The tach in the dash is actually not that far off, maybe 250-300RPM higher. If I can get some time later and it stops raining here I'll try to work on it tonight, otherwise it'll have to wait till tomorrow. I'll post back with results once I'm done. Thanks!

91interceptorZ

iTrader: (3)

to throw another bone in there......I would check the total timing when you get a chance....

fleetmgr

Correct, the only thing the link is for is to shut the secondaries.

92RS_Ttop

iTrader: (3)

Yeah, that's on my to-do list. As soon as I can get my timing light working consistently and the balancer marked.

92RS_Ttop

iTrader: (3)

I removed the bolt in the secondary throttle lever and its MUCH better. Still has a stumble, but it doesn't feel like its about to die on me. I'll try tuning the idle mixture as mentioned above and see if that helps. I'm also gonna move the accelerator pump cam back to the #1 hole as that should bring it in slower if I am reading the profile right.

Would it be worth going back down to a lighter secondary spring, or should I stick with the black spring?

92RS_Ttop

iTrader: (3)

I adjusted the idle like you suggested and now it only has the slightest hesitation left. The bigger problem right now is that I can't just kick it to the floor to go WOT as the clutch slips. I guess that's what I get for installing a used pressure plate and smaller clutch disc(although it is new). I haven't moved the accelerator pump cam yet, I'm gonna try driving it around town tomorrow and see how it runs.

I'm still getting the occasional backfire when I let off the gas, but its no longer a constant crackling/popping when I let off. It only did it 2/4 times, but it was a pretty strong backfire. I'm thinking that it is a timing related issue from some other threads I've read on here, but not sure.

All thoughts/input/advice are welcome, and I thank you guys for the suggestions given so far. Its running a hell of a lot better now.

fleetmgr

I'd leave the black spring in for now until you get the backfire problem taken care of. Getting it running right on 2 barrels, then worry about fast.

92RS_Ttop

iTrader: (3)

I *think* I have the backfiring problem taken care of. It hasn't done it again in 2 days of driving the car. Apparently one of my header connections slipped out of the connection to the y-pipe. I reconnected it back up and tackwelded it in place. I've been having problems with it slipping off. It hasn't backfired at all since I did that, although power is down a good bit. Probably just the extra restriction, its a pretty crappy y-pipe that I just slapped together to be able to pass inspection. I will be redoing the entire exhaust next winter, probably a true-dual 2.25" or 2.5" setup.

Still getting a slight stumble though. I think I may have picked up a vacuum leak somewhere though as it started idling erratically last night after I got home from the store. It would idle fine for a few seconds, then jump by about 300-400 RPM for a couple seconds, then back down. It kept doing this back and forth. I noticed the vacuum gauge was jumping with the RPMs as well from 14-15" to 20-21".

fleetmgr

I'd agree with the vacuum leak. Have you checked the vacuum advance can? What you were calling backfire may have just been the crackling you sometimes get through the exhaust when letting off the gas. My 96 LT1 does this also...guaranteed it's not backfire. Backfire is usually a single loud bang.

I thought when I re-read your original post I thought that your idle vacuum sounded low, especially so with the cam specs you posted.

92RS_Ttop

iTrader: (3)

The advance can is a good possibility. The distributor is used, and while I rebuilt it before installing it, I didn't replace the advance can. I hooked up a handheld vacuum pump to it and it was holding vacuum ok so I assumed it was still good. I'll try disconnecting the distributor and see if the vacuum changes. The other possibility is the EGR blockoff plate I made may not be sealing well. I've been wondering about it leaking since it took me 3 tries to get it on there to where I thought it was sealing good. I don't hear a vacuum leak around it, but that doesn't necessarily mean anything either.

As for the backfiring vs crackling, it was doing both. It was crackling a lot more on deceleration than it did before I started all this. I hate that sound, but I know its not a problem. The backfiring I was talking about though was your typical single loud BANG that sounds like you're being shot at. It was also how I noticed the header being disconnected from the y-pipe on the passenger side. I was tuning the idle, and reving the engine to make sure it was stable and I saw flame coming from the header collector when it backfired.

fleetmgr

When you check the advance can, pull the dist. cap and watch the plate rather than the gauge. If you see it move at all back towards the at rest position, replace the can. I used to just suck on the hose and stick my tongue on the end...easier than rigging a vacuum pump.

Also, check PB booster, lines and check valve.

92RS_Ttop

iTrader: (3)

No apparent leaks in the brake booster/hose/check valve. I pulled the check valve off and there was still vacuum in the booster. The check valve works properly when I blow into it from each end.

The distributor's vac advance works fine as well. I pulled the cap and hooked up the vacuum pump, and it held 10" just fine. No movement on the plate.

I may have had a slight leak from a loose hose connection somewhere since by the time I was done testing some things with the car idling, my vacuum was up to 17". It wasn't idling erratically like before either, so maybe I just had a loose hose connection. I'll get to drive it tomorrow and see how it goes.

92RS_Ttop

iTrader: (3)

Well, I found a vacuum leak. Unfortunately I was about a mile from my house when I found it. The EGR blockoff plate I made wasn't sealed well enough and after a hard throttle run up a long hill, I lost whatever little amount of sealing I had. I managed to limp it home and have it fixed now. Warm idle vacuum is up to 16.5-17.5 but its still bouncing around. I'm thinking of pulling the carb and trying a different sealant on the gaskets.

I was also wondering about the charcoal can. I have an older one from a carbed truck and I have it T'd into the PCV vacuum line. Does there need to be a check ball or anything on the charcoal can line? I don't remember seeing one on that truck, but the V6 that was originally in the Camaro had something that looks like a valve of some kind in its vacuum line.

92RS_Ttop

iTrader: (3)

Still having problems with an apparent vacuum leak. After driving the car for a while, especially around town, or multiple short trips running around town it starts to idle rough and the vacuum gauge starts acting up. It'll idle around 17 and every 7-10 seconds or so it'll drop to 13-14 and come back. After a few times of this if I don't tap the gas pedal it'll die out.

I've searched for vacuum leaks and cant seem to find any. I resealed up the EGR blockoff plate I made, replaced the carb-to-adapter and adapter-to-manifold gaskets. I found my PCV valve wasn't sealing tightly enough to the rubber grommet in the valve cover so I sealed up both with some black RTV and replaced the vacuum hoses used to connect the PCV to the T to the charcoal can and from the T to the carb. When I plug the port that the PCV and charcoal can are connected to on the carb it smooths the idle out nicely, but I don't think I can drive it like that to fully test it. Will it hurt anything to drive it with the PCV and charcoal can disconnected?

Also, I did have an issue with the secondary throttle plates not closing completely before. I adjusted them and they seemed to be closing, but is there any way to check to see if they are closed? I tried closing off the top of the secondaries by holding a balled-up rag over them, and after several seconds it wanted to stall out. When I pulled the rag off, I noticed gas pouring from the secondary squirter. Is that normal?

92RS_Ttop

iTrader: (3)

Bringing this one back.

I fixed the idle problems I listed in the last few posts. I had some sealing issues with that EGR block-off plate and at the base of the carb.

Now, however, it is running really rich at part-throttle. Idle seems to be ok, but when I get on the gas I get a really nasty fuel/exhaust smell. Once I let off and go back to cruise the smell will go away after a few minutes. I pulled plugs 1 & 2 yesterday and they were black on the top ring with some crusty/flaky soot there as well.

Fuel level and transition slot are adjusted correctly, pulling 15-16" vacuum at idle. Using a 75 power valve, and the original 66 jets on the primaries. Vacuum secondaries so its got a metering plate instead of jets. Fuel pressure is 6-7psi and steady.

No other issues other than a slight hesitation when you slap the pedal to the floor.

I'm thinking I need to drop a few jet sizes. Does that sound right?

865sp

what # squirter are you running most 600 come with a #25 , you need to go up to a # 28 or 31, run the orange cam in # 2 hole make sure you readjust the pump arm , to right clearance , use your vacuum gauge to adjust your air fuel mix screws , start with them screw out about a turn and a half , them screw them in or out until you have the most vacuum on the gauge , turn them in or out a very little at a time . set you timing at least 10degree btc. You might also want to go to a pink cam on the accelerator pump cam and run it in the # one spot

sofakingdom

iTrader: (1)

How'd it work out for you after you read annd followed the HOlley Tuning sticky at the top of this forum?

92RS_Ttop

iTrader: (3)

I've got the orange cam, its in the #1 hole. I tried putting it in #2 last summer, and it made the slight hesitation off idle worse. Not much, but definitely noticeable. I had been considering going to the blue cam.

It does have a #25 squirter. If its already running rich though, wouldn't going up to a #28 make that worse? The fuel/exhaust smell is worst when I get on the throttle, which is when the squirter would be in use.

When I set the idle screws last summer, I did use the vacuum gauge. I set it for the best vacuum at idle, per the Holley instructions.

I can't remember what my base timing is at, I set it early last summer and haven't touched it since. I do plan on checking it again later this week. I suspect that my timing curve needs adjusted as well. I'm not getting any pinging, but IIRC base timing is at 8*BTDC with a max timing of 24-28* BTDC at 3000-3200 RPMs. That's mechanical advance only, no vacuum. I was going to see how it liked 10-12* base and try to get it up to around 30-32* at 3000 RPMs.

92RS_Ttop

iTrader: (3)

I followed it as best I could, but without any other jet sizes I wasn't able to do much. I also wasn't sure how well it would work since the sticky seems to be for mechanical secondary Holleys and mine is a vacuum secondary. I don't have a power valve or jets on the secondaries to tune them. To answer your actual question though, the parts I was able to follow definitely helped with the idle quality and got rid of the fuel smell at idle.

I hate to spend money on things I may not need, so I am trying to determine if different jets are what I really need to get it dialed in properly. At $7/pair + shipping, that's potentially a lot of money that I would be wasting that I could spend on other areas of the car. Like the adjustable panhard bar I now need to properly center my 4thgen rear. Not to mention the pump cam kit and squirter nozzles.

pancherj

First of all, you need to get the timing curve sorted out before you even think about touching anything else on the carb. Most likely, the base carb setting are all your car will need ONCE THE TIMING IS SET CORRECTLY. Your base should be in the 12* advanced range. You should use vacuum advance. With is plugged in and your idle at roughly 900RPM, you should have around 46* advance. At WOT, you should have around 36* advance by around 3000RPM.

Do this, THEN go back and set the idle, idle mixture screws, etc. I bet this clears up your rich idle condition. Don't touch anything else on the carb until the timing is right.

92RS_Ttop

iTrader: (3)

Unfortunately, the dial on my timing light only goes to 36* and my timing tab only goes to 6* or 8*. If its supposed to be 46* with the vac advance connected, I'll have to guesstimate it. The engine currently idles at 1000, do I need to turn it down with the idle screw to set the timing, or will 1000 be ok?

The rich condition is at part-throttle, not idle. The idle is fine.

pancherj

You could take a guess at the timing, or get a tape for the balancer to be safe. I still would get that ironed out before moving forward with the carb. And yes, a 1000RPM idle with that cam you have sounds high. To set the timing, turn it down as far as you can. I would think 800RPM is high enough. You want to make sure that the mechanical advance is not activating at all. Also, the problem with getting a high idle speed is you need to open the throttle plates too far. This exposes too much of the transfer slots which leads to a rich idle and rich "Light cruise". You said yours is rich at cruise...what kind of RPM are we talking about? At light throttle opeing (cruising along on a flat road at 2000RPM) almost all of the fuel is coming from the idle circuit. As the throttle opens more, the boosters (and consequently the jets) take over. Finally, when the throttle opens enough and the vacuum drops, then the power valve circuit starts to take over.

To tune the carb, you really need a vacuum gage you can read in the car while driving. This will help determine which carb circuit you are on, help determine appropriate power valve rating, etc.

92RS_Ttop

iTrader: (3)

I do have a vacuum gauge connected in the car. This morning idle was 18.5", coasting downhill in 5th gear it was at 25". I don't remember what it read during acceleration. I'll take it out on my lunch break later today and check the gauge.

When I get the rich smell is when I give it gas while driving to accelerate. For example, coming out of a turn and starting to accelerate or while trying to accelerate going uphill. Usually around 40% throttle or higher. RPMs would be from around 1500-2000 through 4000.

At cruise, its fine. The smell lingers a bit with the windows up after I left off the throttle, but eventually goes away while cruising so I know its not having the problem while cruising.

Transfer slot is where it should be. I made sure I had that set right last summer when I was fine-tuning the idle screws. I am assuming it hasn't moved since then.

pancherj

Good info! At 18.5 to 20", there is no way that the power valve is coming into play. You are looking at the main jets here. I would say you want to step down on the jetting until the rich-issue is solved. This seems straight forward (famous last words!). However, this will probably cause other problems. You may find that your WOT condition is lean. To solve this, you need to increase the size of the power valve channel restrictors (make the opening larger). Also, you may find the car wants to stumble when going to WOT. This is solved by making the pump shooters larger and maybe going to a more agressive pump cam.

92RS_Ttop

iTrader: (3)

That's what I was looking to confirm.

When you say "power valve channel restrictors" I'm not sure what you are referring to?

I have the heaviest spring in for the secondaries, so hopefully it won't go too lean when I go WOT. But honestly I very very rarely go WOT as I'm afraid of destroying my T5 so I'm not too worried about WOT conditions right now.

92RS_Ttop

iTrader: (3)

Took a drive to Subway for lunch. I was watching the vacuum gauge every time I got on the gas, and the lowes it hit was 9". That was only once though, before it was really warmed up. After it was warmed up, it never dipped below 10". RPM range was from idle to about 3500. I drove it like I normally do when I'm driving around town, shifting right around 3000-3200. Didn't get much fuel smell, but then I had both windows down since it was pretty hot outside.

Based on the numbers I saw, I'm going to say the power valve is not coming into play at all here since its a 75. Assuming I have how it functions straight in my head. It only comes into play when vacuum hits 7.5" and lower, right?

pancherj

You have the function of the PV correct. The POwer valve channel restrictions can be seen by removing the block and the PV. In the block, where the PV goes, there are some very small openings. This is where the gas flows into the main wells to enrich the circuit under WOT. These holes may be too small (once you drop your jets down and clear up your cruise). So, you will need some small index-type drill bits and a small hand vice for holding the bits (no power equipment!).

It seems scarry, but you just go in small steps!

92RS_Ttop

iTrader: (3)

To be honest, I am dreading taking the carb apart more than drilling the passages. I hate tearing the carb down and spilling gas everywhere and replacing the gaskets cause they tore(again!) and then connecting everything back up again. Then rinse and repeat cause I didn't make the holes large enough

Here's hoping I can just get away with the jet changes!

Anyhow, I'll order some jets following the recommendations in sofa's sticky and post up the results in a couple days once I've had a chance to try them.

92RS_Ttop

iTrader: (3)

I got the timing set as best i can. Initial is 16* mechanical, and 25* with the vacuum advance connected. Mechanical peaks at 30* at about 2700 RPMs. It won't go any higher than 30*. Idle mix is still fine. As soon as i move either screw to lean it out, the vacuum drops.

I have some jets ordered, just waiting till they get here. Currently have 66's, so i ordered a kit containing 65 through 60. I know the tuning sticky says i should get 68's too, but with it running rich i figured they wouldn't be needed.

pancherj

16 initial is pretty good...25 with the vacuum hooked up is pretty low (is the vacuum canister a stock one from a 1970's HEI?) and 30 total is a little low. I don't think these are causing your problem, but with more vacuum advance and a little more total, the car might run better and have better throttle response. I'd throw 4* more initial in to see how it likes it. 20* total initial may make it hard to start with a factory starter...

92RS_Ttop

iTrader: (3)

I think it may take 20* initial. It really seemed to like 18* initial, i turned it back cause I was afraid it was too high.

Yes, its a stock hei vacuum can. I pulled the distributor from a late 70's/early 80's chevy truck in the local u-pull and rebuilt it. The vacuum can tested fine so i kept it.

Im not sure how i can get more total? Isnt that limited by the travel of the mechanical advance mechanism in the distributor?

pancherj

The vacuum cans that GM put on different motors all acted a little differently. You want one that starts adding advance around 12" and is all done by 20" or so. Thos late 1970's ones need way too much vacuum to strart actuating (it was an emissions thing). You can buy replacement cans at NAPA. Do a google search for the part number of various ratings on the canisters. The one that came on my GM Performance HEI was about perfect.

Your total is limited by the mechanism inside the distributer. In your case, this could be a blessing. You could easily run 20* initial and still not be over on your total. That is a good curve for a performance car. HOWEVER...make sure the distributor is actually done advancing and that it isn't the springs that are preventing it from going all the way or that the mecahnism is sticking. I'd hate to see you bumb up your initial and then rev it one day to 6000RPM only to find your total goes to 45*!

92RS_Ttop

iTrader: (3)

I know the mechanism isnt sticking. It moves nice and smooth when i move it by hand. I doubt its the springs because i went to a lighter setup yesterday trying to get the advance in quicker and the total didnt change. It just comes in a couple hundred RPM sooner

92RS_Ttop

iTrader: (3)

Double-checked the timing today, and put the other "lightest" spring in. So now its running both of the "lightest" springs in the advance kit I had. I'm at 32-33* at 3000 and it doesn't go any higher than 35* all the way up to 4500-5000. The engine will never see higher than 5000. With the valve springs I can't really rev it any higher without running into valve float issues. And the ported 416 heads stop making power at about 4700 anyhow so there is no need to go higher.

I did bump it to 18* initial when I changed the advance spring, and was able to get the idle down to around 750. Throttle response seems a bit better. No signs of pinging when I drove it all over the place tonight. I put about 50 miles on it testing it up and down hills, on flats, accelerating out of curves, everything I could think of to make sure the timing wasn't going to cause a problem. So now I'm just waiting on the jet kit I purchased. Should be here Tuesday or Wednesday.

92RS_Ttop

iTrader: (3)

Sorry that ias so long, but I want to include as much info as possible to make sure I've got it right.

So I got my jets today and started playing around. The carb had 66's stock, so I started with 63's. Not much of a difference, less fuel smell though. Car idled and drove fine. Dropped to 61's and no real noticeable difference there either. Tried cruising up a long steep hill by my house at 60mph, and didn't notice anything I would describe as "surging" although to be honest, I'm not entirely sure what it would feel like while driving. I'm very familiar with it at idle as my truck has done it ever since I swapped the cam and put headers on it(vac leak or ECM tune, I'm not sure which yet-probably both). About 1/3-1/2 way up the hill I noticed what seemed like clutch slippage, but no changes on the tach or vacuum readings. Clutch has never slipped before and only has 4k on it. I am assuming this is the "surging" I am looking for. Just to be sure, I put in the 60's I had gotten as well. I know 1 size is a tiny, tiny step, but it did the same thing going up the hill. Maybe a slight bit worse this time. So I went back up to 62's and ran the hill again. No noticeable problems, car went up smoothly except for the ever-present potholes and ripples in PA roads. Still getting a slight fuel smell with the tops off and accelerating with the 62's. This was at 10" of vacuum so the power valve definitely wasn't open. Much less of a smell than before though.

Power valve is currently either an 85 or a 75. It has an 8 a 7 and a 5 all stamped on the same side of the valve. The 7 is at the 1 o'clock position, the 5 is at 3 o'clock, and the 8 is at 9 o'clock. I'm going to assume its an 85 since those numbers are straight across from each other, but please let me know if I am wrong.

pancherj

Welcome to the world of Carb tuning! Dropping from stock 66's to 61's is a pretty big jump. I am actually suprised that the engine wants such little jets. However, I have never messed with a 600cfm vacuum secondary Holley. I will say this...you are entering that area of the fuel delivery curve where I like to have a higher actuating power valve and leaner main jets. This is where Holley's rule of "1/2 idle vacuum for power valve" really doesn't work (except maybe on a race car). Going up that hill and regestering 10" of vacuum tells me you should have a 10.5 power valve (because it really sounds like it is a lean surge you are experiencing). If you do this, you can keep the 61 jets for a leaner cruise AFR (when your vacuum is between 12 and 20"). Try it and see what happens!

Phoenixfire1989

I'm having a similar issue that the performance shop caused..it's been that way for over 2 weeks. I've got the backfiring down to only when it's kinda cold. Unfortunately, i'm not mechanically inclined to be able to fix it.

92RS_Ttop

iTrader: (3)

So i finally got my power valve yesterday and I put it in today. Went for a test drive and the car is running like crap, and it sounds like I dropped a few rocks into the engine. I nursed it back home(only went about a 1/4 mile or less round trip) and shut it down. Checked to make sure I didnt leave a tool under the hood and started it back up long enough to recheck my timing. Timing hasn't changed, still at 18* at idle with the vacuum advance connected.

The car ran fine just before I changed the power valve so I don't think I threw a rod or anything major like that although the engine sounds that way. What I'm wondering(read:hoping) is that my old power valve was leaking and thats why it was running so rich and I was able to step down the jet size as far as I was. I'm going to try swapping the old power valve back in once the engine cools off a bit and hope it goes back to normal.

I know you're supposed to be able to test the power valve for leaks by turning the idle screws all the way in to see if it dies from lack of fuel, but is there a way to test a power valve when its not in the carb?

92RS_Ttop

iTrader: (3)

Put the original power valve back in and its still knocking Not that I really expected it to go away. I was just kinda hoping it was running really lean due to the new power valve not leaking. Guess ill be pulling the engine soon