I have a 57 312 Thunderbird with Fordomatic A/T that idles roughly at anything less than ~900 RPM. It will idle at ~500 RPM but is quite rough. Everything is stock on the engine. New plugs, points, condenser, cap, rotor, 26 degrees dwell, 8 degrees timing advance with the vacuum advance disconnected. Idle set as well as I can get it on the carb.



145 to 150 psi compression on all cylinders except one is 125 psi.



When I start the car the manifold vacuum is steady at about 17 inches Hg at idle. As it warms up it drops to a steady 14 inches Hg. The idle gets worse as it warms up.



Any suggestions? My guess is a burned valve on the cylinder with 125 psi compression. I would not think that would be bad enough to give a crummy idle though.



thanks

Dave Christensen

Dave Christensen

Falllbrook CA

57 Tbird