Troubleshooting lean idle

[Canadian1968]

There has to a problem somewhere . I don't think it is the carb. Your carb is set wrong obviously but that because it's trying to cover up the real problem . The motor.has been rebuilt and some thing has changed somewhere . The problem DOES still sounds like a vaccum leak. The question is where . I would eliminate the carb since you have tried so many ,.can't see you making the same mistake over and over with the carb. But work your way down. Check intake bolts, valley pan position , does it have power brakes check vaccum connections and lines . Also set your timing correctly move it to where it should be don't diagnose with it set at 40.

You say it clears up as soon as you hit the gas so hopefully that counts out anything major internally or crossed plug wires .

 

[Napoleon1991]

I've never had much luck spraying solvents looking for leaks. Might have to use a smoke machine.

Just tried a smoke machine on it with no luck. Couldnt find a leak anywhere

 

[Napoleon1991]

There has to a problem somewhere . I don't think it is the carb. Your carb is set wrong obviously but that because it's trying to cover up the real problem . The motor.has been rebuilt and some thing has changed somewhere . The problem DOES still sounds like a vaccum leak. The question is where . I would eliminate the carb since you have tried so many ,.can't see you making the same mistake over and over with the carb. But work your way down. Check intake bolts, valley pan position , does it have power brakes check vaccum connections and lines . Also set your timing correctly move it to where it should be don't diagnose with it set at 40.

You say it clears up as soon as you hit the gas so hopefully that counts out anything major internally or crossed plug wires .

I have double checked the intake and even replaced the valley pan to rule that out. I unplugged the power brakes and plugged that port to eliminate that as well.

 

[beanhead]

Try a known good coil. Possibly other ignition issue--ecu maybe.
Bad/failing coil will do exactly as you describe. A/F will read lean with misfires as the O2 sensor detects the amount of oxygen in exhaust stream.

 

[Napoleon1991]

Try a known good coil. Possibly other ignition issue--ecu maybe.
Bad/failing coil will do exactly as you describe. A/F will read lean with misfires as the O2 sensor detects the amount of oxygen in exhaust stream.

Already tried 3 coils and 2 distributors

 

[Napoleon1991]

Is there any chance this problem is cam related? I reused the cam and lifters i had in it before the rebuild because they had very low mileage and appeared to be fine. I put every lifter back in the bore it came out of. It doesn't seem cam related because the engine runs fine at higher RPMs, but I am running out of possibilities.

 

[Curiousyellow71]

Your compression check says the cam timing may be fine but that also depends on what the static compression is..? If the cam timing is retarded it can idle rough like described.

 

[Napoleon1991]

Your compression check says the cam timing may be fine but that also depends on what the static compression is..? If the cam timing is retarded it can idle rough like described.

Static compression is right at 10:1. The cam was degreed when I first built the engine, but I did not do it again the second time around since I reused it. It does have a new crank in it, but I wouldnt think that would make a difference.

 

[Don Frelier]

The crank could make a difference you are assuming the keyway is in the same degree angle. It could affect your tdc damper mark as well.

 

[Curiousyellow71]

If its a honest 10:1 and fresh I would expect it to be 180ish.? If the cam timing was retarded that could be why you show 160...or you just may not have 10:1 and are in the mid to lower 9s???

Electrical problems...such as plug wires w too much resistance can do funny things. Visibly they can look fine and cause trouble. Usually electrical problems show up under load, but weird things happen w electrical issues. It sounds like you have tried a lot.... Have you tried plugs and wires? bad engine ground?

 

[Napoleon1991]

If its a honest 10:1 and fresh I would expect it to be 180ish.? If the cam timing was retarded that could be why you show 160...or you just may not have 10:1 and are in the mid to lower 9s???

Electrical problems...such as plug wires w too much resistance can do funny things. Visibly they can look fine and cause trouble. Usually electrical problems show up under load, but weird things happen w electrical issues. It sounds like you have tried a lot.... Have you tried plugs and wires? bad engine ground?

The compression is a little over 9.9. I have not replaced the wires, but I have checked each one and nothing appears to be out of the ordinary. I've also pulled all of the spark plugs multiple times and checked for cracks and checked that the spark plug gap is correct. Engine ground is also good.

 

[Curiousyellow71]

You could try a different heat range of plug and see if it changes it. Did you do a resistance check on the wires? What are you running for plugs now?

If you want to know about what your cranking pressures should be...you can use your numbers in this calculator and see. 160 may be ok since there are several variables.
http://www.wallaceracing.com/calc-crank-press.php

 

[Curiousyellow71]

Also a good idea to double check your timing light... if you have not already. They can go bad.

 

[That_Tall_Dude]

The crank could make a difference you are assuming the keyway is in the same degree angle. It could affect your tdc damper mark as well.

Didn’t he say the confirmed balancer mark was correct, and the piston was at TDC? (was not stated how that was confirmed though)

Wouldn’t a shifted keyway be seen checking that?

(Edit: typos/grammar corrections)

 

[That_Tall_Dude]

I disconnected the brake booster and plugged the port on the intake to rule that out. I sprayed starting fluid around the intake and carb, but it made no difference. The damper is only 2 years old and TDC has been verified. This problem really has me stumped.

This

 

[Wietse]

Do you have a PCV valve? What is your idle vacuum?
If your idle vacuum is low or valve is stuck/broken there is a chance the PCV is in the full-flow mode and allows a ton of air in at idle.

 

[Napoleon1991]

Sorry its been so long since i replied. Been too busy to work on the car until the last couple weekends. To answer some questions, i already checked and replaced the pcv. My idle vacuum is around 17 and the needle is steady. TDC was verified with a degree wheel and a piston stop. Since i was planning on changing cams anyway, I swapped the cam for a voodoo 703 i had, and the problem is significantly better in addition to have tons more power and throttle response. I degreed the cam amd it matches the advertised specs. I still cant figure out my overly lean idle though.

 

[Wietse]

Check that the secondaries on the carb are closed.
If they are cracked open they allow dry air in that leans out the mixture.
You can try and stick a rag in the secondaries at idle and see what the changes are in idle rpm and AFR meter. (assuming you are using one)

 

[Napoleon1991]

Check that the secondaries on the carb are closed.
If they are cracked open they allow dry air in that leans out the mixture.
You can try and stick a rag in the secondaries at idle and see what the changes are in idle rpm and AFR meter. (assuming you are using one)

Already tried that as well as a couple spare carbs I have with no improvement.

 

[Paul_G]

It is getting un metered air from somewhere. If it is not above the intake where you can find it, look below the intake. Could be a bad seal on the intake ports, on the valley side. Look for signs of oil being sucked in to the intake ports. will have to pull the intake to see. If you have exhausted all other ideas.