gm305 1978 unstable idle rpm

[sarantis]

When cold the engine runs very smoothly at idle.When warm at idle the rpm varies.Can you suspect possible reasons for that?
The distributor is a Mallory one ,i 've set the timing and dwell properly,the carburator rebuilt by an expert.Does the coil may be responsible for that?
Thanks in advance for any replies.

 

[Haut Medoc]

Re: gm305 1978 unstable idle rpm

Have you looked at the choke when warm to see what it is doing?......
It sounds like a fuel issue, not an ignition isssue.....
It is not the coil.....​

 

[sarantis]

Re: gm305 1978 unstable idle rpm

Choke is working properly.Can't be an electrical problem?

 

[Maclin]

Re: gm305 1978 unstable idle rpm

I would suspect a vacuum leak. A vacuum leak is not as apparent with the choke on.

 

[Haut Medoc]

Re: gm305 1978 unstable idle rpm

Choke is working properly.Can't be an electrical problem?

Nope.....
I concur with the possible vacuum leak......
Do a vacuum test.....