Running Rough

[kev75stingray]

Hi, Im new to the form and just purchased my first vette (75) a few months ago and am pulling it out for the first time, but its running kinda rough.

I started it and let it run for about 10 min., it was at about 400rpm, took it for a little spin and it soon idled at 1500rpm and constantly blows black smoke. After a while the rpm's dropped to about 1000. When I finally shut it off, it kept runnin for 5-10 seconds after the key was off, so im guessing the timing is out.

What would cause the black smoke and the changes in rpm. Any help or tips on tuning it up would be greatly appreciated.

 

[Camtwister]

First of all welcome to CAC. The most helpfull / friendly community there is. The black smoke is due to a rich mixture. The increase in idle speed is probably due to "cleaning out" the cumbustion chambers / leaning out and then the overly rich mixture causing it to run rich and decreasing the idle speed. The dieseling is probably due to the high idle speed. Have you looked at the choke to see if it is operating properly? Does the choke pull off work? Does the car blow black smoke any time you accelerate or just at idle or as you accelerate from idle?

 

[kev75stingray]

The black smoke is constant during idle and acceleration. I havn't really looked at the choke yet, im still getting used to the whole carb. thing, im used to fuel injection. Im guessing there's just a screw to adjust the air/fuel mixture?

 

[Chick]

cough choke gag

Look at the choke pull off, that's where your problem lies. It can cause all your symptoms.

At cold start is the choke plate cracking open better than a quarter of an inch? I don't think your vacuum choke pull off is working.