C2 - 1963 - 327/340 hp rough idle problems

[Harry L.]

Hi gang!

My 327/340 runs great for about 25 miles or so. After it warms up (180*) It starts to idle rough and starts to load up. At times it even stalls. The idle is set at 800 but when it starts to act up it goes down to 500 and runs terrible.
I have had the carter afb 3461S carb looked at by two reputable mechanics and was told that the carb was fine. I had a compression leak down test done, adjusted the valves, replaced the intake gasket, complete tune up, made sure the distributor was installed correctly,even put another carb on it to make sure. And the problem still persist. Now, when the carb was off I noticed that the driver side back port on the intake was carboned up. The other three ports are clean(No carbon). Also, after the car is shut down, it smells of gasoline stronger than I think it should. But the carb guys say it is normal for an open fuel system.I don't know about that. All I can think of is if the intake warps when warm causing it to leak? I am at ends with this and any input would be appreciated.

Thanks: Harry

[Brian Monticello]

Re: C2 - 1963 - 327/340 hp rough idle problems

Is your heat riser opening all the way? Is your choke off all the way? Check these two things first as both the cause and symptoms are related engine temperature.

Brian

[Duke W.]

Re: C2 - 1963 - 327/340 hp rough idle problems

Per Brian the heat riser valve is the #1 suspect. When the engine is cold see if you can move it. Even it it works try wiring it open.

Also, what are the numbers on the vacuum can mounting bracket? The OE "201" can was not well matched to the engine's manifold vacuum characteristics. It will not keep the vacuum advance locked at full advance at idle, which can lead to the idle instablility you describe. The normal idle vacuum is 900/12", but the OE vacuum can does not provide full advacne until 15.5"

Recommend the '64-up SHP/FI vacuum can - Delco 236. The NAPA Echlin VC1810 is a functional replacement - costs about 10 bucks, and it can be replaced w/o removing the dist. This can provides full vacuum advacne at 8", so it will stay locked full on at idle.

Duke