I recently replaced the exhaust manifold...new gaskets etc...I am having a challange in getting the idle down. (Had this problem before the exhaust manifold change)Is it possible the vacuum advance unit at the distributor is bad-?? would this cause this-?? I have all connections tight...Linkage at carb is all the way out....can't get the idle down, Vacuum leak someplace-?...Suggestions-?
Thanks,Dennis
On my '37 the linkage is worn so I have to attach a spring near the idle adjust screw to return it to idle until I get repair parts. I just changed intake and exhaust gaskets at the manifold and idle was unaffected. I do have my wiper system vaccum plugged off at the carburetor.
The worst time I had with the idle not going down was with a vacuum leak so looking at that would be the first thing I'd do.
You might try plugging up the wiper and advance lines at the manifold to see if that makes a difference. The next step after that is to spray some petroleum product like WD-40 at the various intake manifold connections while the engine is running. If you spray an area that is sucking in air the engine will change how it is running.
As the others have mentioned look for an air leak, a worn throttle plate shaft is also a common culprit, if you can wriggle it and change the idle speed without moving it off the stop it will need rebushing. If you're not sure spray something around it as Tod mentioned, kerosene or even soapy water will do.
Take the needle valve out and look at it. I had one that would n't idle because the needle valve wasn't a needle
Another thing to check is the high idle linkage. This is the piece that is a spiral ramp that makes the idle stopscrew rest higher when your choke is on. Mine has a burr on it and sometimes it will not return to its disengaged position when the choke is completely open. You didn't mention what year your car is so I am speeking from the basis of the Carter B1B carburetor. You can mechaicall ydefeat this with a tie wrap or zip tie to see if it might be your poblem.
Also make sure you choke is fully opened when not needed. Carb gasket is good shape and carb to manifold tight??
Re: Idles too High- I was able to move the throttle linkage just like...an 1/8th of an inch more in that direction at the end of the travel-and the idle came down..to a much better level...I washered that rod to hold that amount of adjustment and it seems to be fine. This is a 39-P-8
Good job! You might need a spring too.
Jim