Alabama65stang
Well-known member

Still trying to solve a rough idle. 800 miles on fresh rebuild, Comp 260 cam, Holley Weber carb, DuraSpark II with Blaster coil, C-4 tranny. Idle is erratic, vacuum moving between 13-14". I have sprayed everything with WD-40 , no indications of a vacuum leak. It is not a dead miss and pulling the plug wires one at a time does not indicate a single cylinder causing the problem.
I did notice today with the breather off at idle, gasoline drips out into the venturi onto the top of the butterfly. I backed off the idle throttle screw and the gasoline flow seemed to have to stopped but still had the rough idle. Can't leave it there because it gets real rough in gear. Idle mixture screw is about 3 turns out, a little richer than lean best idle.
Spark is about 25^ initial advance with the vacuum can hooked up to the manifold.
Everything runs really good above about 1000 RPM.
I still have the stock 1 3/4" exhaust system and muffler, could this, in combination with the cam be a suspect? Back pressure does not seem to be a problem at higher speeds and it runs well up to 80 MPH.
Anybody got any ideas?