I am having the following problem with my 305 4bbl carb'ed camaro.

When I try to start the engine after it has been sitting around for a while(6 hours or more), it will start, RPMs will go to about 750, within seconds drop to 500, engine sputters and stops.

I tried giving it a little gas to keep the RPM up, but it stopped anyway.

After a few minutes or a few starts, the engine will start to run smoothly at about 750-800 RPM.

This morning, the thing idled at 1500 RPM!!

I thought this might be a fuel pump or IAC issue. Any other ideas?

Any help would be cool.

-Matt

 

Could be a sticky choke....just a guess

 

Matty,

There is no IAC, ,per se, on a carbed system. There may be an idle solenoid or two, but no true bypass-type IAC. The solenoids are more commonly referred to as an ISC - Idle Speed Control.

I'm guessing you have a mixture issue as well, which could be the result of many things:

Float level incorrect;

Choke not operating;

High idle cam not operating (although if it idled at 1,500 on a cold start it sounds like it's set almost perfectly);

Poor fuel pressure from a pump or clogging filter;

Vacuum leak;

M/C solenoid inoperative or misadjusted;

Passages in carburetor dirty or restricted;

Leaking fuel well plugs on the bottom of the carburetor (overly rich condition and flooding).


The next time the engine is cold, remove the air cleaner cover before starting the engine and observe the choke operation.

 

Ok, my camaro is still randomly idling low on cold starts, not so much as before, though after running some FI/Carb cleaner through the fuel system. I thought this might be a choke problem like you said, but the choke looked like it was operating ok, so I dismissed that possibility for now. Before I go adjusting float levels and disconnecting vac and fuel hoses, I wanted to run the following by you guys.

From my air cleaner snorkel, on the bottom under the vac motor, the hot air intake hose coming from the exhaust manifold is cracked right through. I was wondering how much pressure goes through this hose because it still lines up with the outlet on the exhaust manifold and if there isn't much pressure, this leaking probably isn't the problem.

Let me know what you think and if this might be my cold start problem culprit.

 

It isn't "pressure" per se, but rather it draws air in through that tube that has been heated by the exhaust manifold. That helps the gas evaporate in the intake manifold a little better when the engine is cold. It's typically more of a problem when the weather is cold, and I doubt it would be the cause of a problem after sitting for only 6 hours. And, since it takes a little time for the exhaust manifolds to heat up, it doesn't do anything immediately after the engine is started. In fact, two years ago I ran my car all summer with an open element air cleaner, meaning that tube wasn't even there.

Try things like replacing the fuel filter. It should have the type that has a rubber check valve in it. That prevents fuel from syphoning out of the carb while sitting.

It is also possible you got a tank of poor quality fuel, or improperly formulated for the current weather (happens - the formulation changes throughout the year).

 

I adjusted the idle screw so my car would idle around 1000 RPM. Personally I thought that was a little high, but it ran smooth. That wasn't a cold start though.

When I took the air cleaner off last night I had my cousin look at the choke. He tried pushing it shut and it wouldn't close. I pumped the pedal to the floor once and it didn't close on it's own(It should, shouldn't it?), but he could push it shut now, once he let go, wide open again. Then he got out of the way and i started the car. He said the choke plate didn't even move, just sat wide open. It looks to be connected to the lever that pulls/pushes it closed/open, just has no tension and doesn't move on its own.

Would this be my cold start idle problem and does anyone know how to correct this?

(Should I move this question to the carb board???)