My engine was installed yesterday, and finally started today. "Break in" went well, but now it won't idle. I'm told its very very lean, and if they cover the top of the carb with their hands it will smooth out. It apparently runs good at other RPMs. He's going to dig back into it tomorrow (I may shoot over with another carb I have also). Any idea's before we open the carb up?

Stock build, .30 over, duplicate of stock cam. The Quadrajet is correct for the car, and was rebuilt by QuadraJet power a couple of years ago, and was running fine before the engine was pulled 7/12/22. It has been sitting since. Base gasket? He's already checked the vacuum lines.

 

Are you saying the engine idled ok during break-in and now it won't or it didn't idle ok at all since the rebuild? Sitting for two months shouldn't be a problem.
Has the timing been set with a light and the distributor hold down tightened?

Try revving the engine and quickly forcing the choke blade shut a couple of times until the engine almost stalls and then let it clear the richness.

It could very well be a vacuum leak particularly at the intake gaskets. Were the heads milled or the block decked?

Good luck!!!

 

No it never idled after the rebuild. Not sure what they set the timing at but it was set up at 7d BTDC. They did the break in and went backed off the rpms to idle it goes rough and stalls. The heads were resurfaced and everything else checked for flatness. I was wondering about a potential intake leak, but I'm told it runs great at other RPM's. Something is making it super lean at idle for sure.

 

Thoughts that came to mind-

Vac leak at carb or intake gasket? Vac measurement checked?

Timing double checked?

Timing mark accurate on balancer?

Cam degreed?

Little piece o’ crap plugging idle circuit?

…

 

I would start with the easy stuff first . Put a vacuum guage on it and play with your idle mixture screws on that quadrajet. Could be as easy as richening up the mixture at idle.

 

^^^this!!!!!!!!!!!

 

If they can cover the carb with their hands and it stays running you have a vacuum leak. Find and take care of that first.

 

Not necessarily. Covering the carb is no different than closing the choke plate. In either case, if the car runs better, it's indicative of a lean condition. It COULD be a vacuum leak, or it COULD be misadjusted idle needles.

 

I’m leaning toward a vacuum leak or something clogged up in the carb sitting which I doubt but certainly possible. Could be some crap in the carb too. Timing is set right. The mixture adjusts do help some. Going to change the base gasket and if that doesn’t work I have a rebuilt 67 carb We’re going to try to eliminate that. If not it’s got to be the intake gasket. All the vac lines are plugged. The vacuum advance appears to hold also. Thx for the suggestions. I’ll report back.

 

I am adding my vote to the vacuum leak group. If the carb only sat for 2 months that should not have hurt a thing. Is this on your 66 ? Does that intake manifold have the exhaust crossover under the carb gasket that requires the thin metal insulator plate ?? Leaving that out will make it idle terribly.

 

Thanks! Yes on my 66. I had changed the carb (was off a 67) to the right 66 carb a couple of years ago. I don’t recall anything under the carb? Just the gasket directly to the intake? It idled fine before the rebuild. What’s the thin insulator?? I can look in my chassis manual when I get home.

 

If it was ok before the build then it is probably fine now. Some Q-jet manifolds have a small passage across the front that exhaust gas runs through. They require a thin stainless steel shim that goes down before the gasket. I attached a picture of a Chevy intake that shows the "slot" I Just did a carb for my Cousins 400 and it had the shim on it but I dont know if its correct because I dont have the car to look at. Yours might not have it. Joe P would probably know.

 

I see. You know I don’t think mine has that. I recall it was flat

 

That slot is a Chevy thing, but I have had a similar problem trying to put E-brock carbs on some OEM manifolds, however. On manifolds where the carb flange is tightly contoured around the bores, you sometimes need a plate to seal the edges.

 

Thx Joe!

 

Well, after starting from scratch and checking everything again, we decided to put 5 gallons of fresh gas in and the original carb back on (which also had the same problem). Low and behold, it runs right. I don’t know if it was the base gasket (replaced for a third time) or gas, but it’s idling smoothly. The gas was only sitting since the second week of July but who knows. I can place my hand over the carb, and nothing happens! Yeahaw! Thanks for the tips and advice.

 

A happy ending! Cheap, though somewhat aggravating and ultimately easy. Now you can have some fun.

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