QuestionDick: I wrote to you around July concerning an idle problem. First, I would like to thank you for the prompt responce. Here is the problem as we discussed. Rebuilt the carb; found gummed up idle circuit jets. Seems to idle better but not correctly. Tried the cardboard (sliding over the carb.)the idle becomes perfect when the mouth of the carb. is 50-60% covered. OK there is a vacuum leak / the intake and exhaust gaskets are new. There is no vacuum advance on the distributor and the wipers are electric. Possible crack in the intake manifold or is the carb. still the problem? Thank you again for your time.
AnswerI see from the fact that this question is still in my in-box that once again, the all-experts site has lost my answer to you that I sent out this morning. NUTS!
OK< here goes again: Yes, you have a vacuum leak - a bad one! I doubt that it is the carburetor, but check that too. Most likely, a plug is missing from the intake manifold (check for screwed in pipe thread plugs, 1/8" NPT threads) or any other orifice on the intake manifold that isn't plugged.
The vacuum line to the distributor is for ported vacuum (not in play at idle) so that isn't your problem.
You'll have to track this down by using a propane torch (NOT LIT!) with the engine idling (carburetor not blocked off - let it run rough) to flood the area around the carburetor base and the intake runners, especially where they bolt up to the block - you'll find either a warped intake manifold (most likely cause) or a bad gasket (slipped when installing the manifold) or a leak between the base of the carburetor and the manifold, or a leak between the cast iron throttle body at the bottom of the carb and the main body of the carb - (bad or wrong gasket, or mis-positioned). Where ever the air is getting in, supplying propane in the area will make the engine rev up as long as you hold the torch there - you can track down the location of the air leak that way.
It is also remotely possible that the throttle shaft bushings are so worn in the caruburetor that they are allowing air to be sucked in there - but that would not likely be this bad a leak. Propane will find it for you.
if the intake manifold is warped (very common on these engines), pull it off and take it to a machine shop and have him mill or grind it flat to within 0.005". It would be best to have the exhaust manifold assembled to the intake manifold when he does this, and have him surface the exhaust manifold at the same time - to save yourself a leak there also. While he is doing that, you surface the block with sandpaper to make sure there is no gasket residue or other debris to make the manifold not fit up tight.
Let me know what you find, please?
I hope this gets back to you this time - my fingers are getting sore!
Dick
