66 327 idle issue

[Paul K.]

my 66 327/350 hp Holley carb starts well, has a good 1600 fast idle. once i start driving, idle will not stay at 750 till engine is run for 15-20 minutes of driving, until then it idles at 550 -650, what can be done to correct this problem

Paul Klemetson (37278)

[Richard M.]

Re: 66 327 idle issue

Paul,

The first thing I'd look at is the Choke and the associated linkages and parts. If the idle stays that low after a initial few minute warm up, it may just be running too rich because the Choke is not opening as the engine temperature rises.

I'd remove the air cleaner, do a cold start and observe what's happening to the choke system and butterfly after a quick warm up and throttle pedal blip to kick down the choke mechanism. Maybe the choke bimetal spring is weak or hanging up.

Another thing to check is the Choke Pull-off diaphragm and linkage. It ensures the butterfly opens a bit at startup. It's vacuum activated from manifold vacuum.

[Gerard F.]

Re: 66 327 idle issue

Paul,

I've been through your problem on my 67/327/300 with a Holley 3810, it is very frustrating. After many hours of tuning and adjusting the carb, I found the problem was a vacuum leak in the vacuum advance tube to the distributor.

I would put a vacuum gage on choke pull-off or vacuum advance line to see what you are pulling at idle. If the vacuum is low at idle when you are hot, you are just dripping fuel into the carb. It will run rough up and down and then die.

I found that the repro stock vacuum tube between vacuum advance on the distributor and the vacuum tube from the carb was too loose fitting. Tried a smaller diameter vacuum line and the vacuum went up, my problem was solved.

It could also be vacuum leak in the choke pull-off or in the carb base plate itself. But if you have low vacuum at idle when hot you need to resolve it

[Paul K.]

Re: 66 327 idle issue

thank you guys for your help.

Paul

[Tim E.]

Re: 66 327 idle issue

Paul - In my case, I had a rough idle as well. My throttle butterfly shafts (or more likely the holes in the base plate) were worn causing a vacuum leak. Jerry mentioned this in his post above. Since I had a spare I didn't need to look into various repairs that I understand are available. Tim