C2- HELP! Idle quality problem

[Glenn Ochs]

I have a 67 Coupe with 300HP-327,powerglide and air cond. All the major components are original. I have had trouble gettting it to idle properly since I got the car. It has the Holley 3810 carb which I have re-gasketed and checked over. You can attain a fairly decent 800RPM idle until you put it into gear,when it will drop below 500RPM and almost quit. If you use the air at this time it will quit. The timing is correct,the advance is working and the ignition is the pertronix type.The PCV is working, the base gaskets are correct, and everthing is hooked up factory original.It doesn't appear to be an engine miss. I really need some new direction on this, it's almost undriveable at this point, unless I get the idle up over 1000RPM.

I also notice it is very hard to start after sitting more than a couple days. Have to pump the heck out of it to get going after a week. The choke is set right and does what it is supposed to( fast idle etc).

Thank you very much for any direction or correction you can offer on this matter.

[Wayne W.]

Re: C2- HELP! Idle quality problem

That thing should idle as smoothe as silk. Its difficult to tell from your description , but I would look at the carb. Do you have a gasket and the SS plate on the carb base? Also look for vacuum leaks. If possible substitute a known good carb.

[Clem Z.]

Re: C2- HELP! Idle quality problem

check to make sure that the idle transfer slots are not open more then .020/.040 when you set the idle. check to make sure that a correct genuine holley power valve is in the carb. check to make sure that the main body surfaces are flat,where the throttle body and metering body bolts on. also check the metering body and throttle body for flatness. more initial spark advance may help because this will allow you to close down the butterflys if the transfer slots are open too far.

[Glenn Ochs]

Re: C2- HELP! Idle quality problem

Wayne: The base gaskets are the heat treated composite on the manifold and then the S/S plate. I also have plugged the heat transfer holes in the manifold recently, it was not right before this though. I'll take any suggestions on where to check for vacuum leaks. I can't really think where I'm going to find another carb. Any suggestions on which Holley models might be allright to try? Thankyou very much

[Glenn Ochs]

Re: C2- HELP! Idle quality problem

Clem, pardon my lack of knowledge but, what are the idle transfer slots and where are they adjusted? The power valve is a new Holley part. The gaskets between the metering block and float bowls are new and seem to have a complete seal.

[Clem Z.]

Re: C2- HELP! Idle quality problem

the idle transfer slots are in the baseplate and can only be seen with the carb off of the engine. set your idle speed and then remove the carb from the engine,make sure that the fast idle cam is not in play,turn the carb over and in the front throttle bores there are vertical slots about .020 wide that show below the butterflys. only about .020/.030 of this slot should show below the butterfly.it should almost look like a square hole,.020 X .020. any more you will have idle quality problems as too much fuel is coming thru the idle transfers and and is not being controlled by the idle mixture adjustment screws on the sides of the metering body. i would recommend you set these slots at .020/.030 with the carb off of the engine,reinstall the carb and see if the idle speed is high enought. if not adjust the idle mixture screws and if you can not reach the correct idle speed you will have to check things like the timing etc.

[Glenn Ochs]

Re: C2- HELP! Idle quality problem

Clem... I'll try get a look at the base plate/transfer ports this evening. I can tell you the LH(driver) side idle adjustment(in front float bowl)screw seems to have no effect on the idle whatsoever. The pass side however, is very sensitive to adjustment. Can this be relative?? Thanks again

[Clem Z.]

Re: C2- HELP! Idle quality problem

that could be caused by not have a good seal between the main body and the throttle base plate. check both for flatness. most of these older carbs need the all mating surfaces machined flat to get a good seal.

[Doug Flaten]

Re: C2- HELP! Idle quality problem

Not positive on this model carb, but if the butterflies have ever been removed from the shaft, they may not have been installed and aligned properly in the throttle bore. So yes, one butterfly can be off center while the other is true. If you find throttle shaft or bushing wear as Clem mentions, you'll have to remove the butterfly throttle plates to remove the shaft.

[Ray C.]

Re: C2- HELP! Idle quality problem

I just had the same problem with a WCFB (thanks Jim) and found that the throttle plates were not closing tight and causing a vacuum leak. After adjusting throttle plates the vacuum reading increased from 17 to 20 and I could control the idle using the idle adjustment screws. The engine now idles fine and there is no hesitation when taking off from a stop.

Ray