Carburetor tuning help
Thread Starter
Instructor
Joined: Sep 2018
Posts: 165
Likes: 64
From: Lakeville MN
Carburetor tuning help
I have an Edelbrock carb on a 79 4 speed that never seems to have the same idle speed from one day to the next. I’ll set it at right about 750rpm and same for when a/c is on with idle solenoid is active. Then once the car is fully warmed up it’s up to 900 or almost 1000rpm at idle. I’ve adjusted the idle when cold and hot engine. It may stay put for a day or two, then it’s off from what I set. Engine always runs and idles smooth as silk. Driving me nuts! No vacuum leaks that I can find, all lines are new. Any ideas?
Last edited by Gralls4771; Aug 4, 2020 at 11:38 AM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Most likely, your throttle cable is not allowing the carb linkage to come completely back to a hard 'stop' position. Disconnect the throttle cable from the carb, hold the throttle closed, and start the engine. Move the throttle a bit open, then close it several times. Was the rpm at the 'closed' throttle position the same every time? If yes, find and fix the problem with the throttle cable. It may be that it is adjusted improperly and won't go to full closed position. If idle is still uneven, do that test again; but this time manually force the throttle closed (rather than just allowing it to close). If it closes properly every time doing that, there is something binding in the carb....most likely a throttle plate which is rubbing the its venturi bore when almost closed. You might be able to see some metal-to-metal rub marks on the offending throttle plate. It could also be in the linkage on the side of the carb. But the problem would be in the carb, somewhere.
If even that method provides different idle speeds when the throttle is held closed, the problem is still in the carb....but it's deeper than a rubbing part. You need someone with some rebuild skills to identify the fault.
If even that method provides different idle speeds when the throttle is held closed, the problem is still in the carb....but it's deeper than a rubbing part. You need someone with some rebuild skills to identify the fault.
