Pretty in Pink, dunno why
Join Date: Feb 2009
Location: Redondo Beach
The symptoms you describe are a sign of erratic idle mixture, and the cause is often a vacuum leak somewhere.
I guess one obvious question is whether or not the idle mixture has ever been fiddled with. They are a bit on the lean side from the factory. If the idle mixture has not been fiddled with, fiddling with it to make it richer might cure the symptom (though not the direct cause if wear is the issue). Remove the plug over the idle mixture screw and gently seat the screw, then turn it out two turns. If it gets better, well, it's better. If it does, there is a method to get the mixture pretty much dead-on that we can talk about.
Looking at wear being the cause, you could grab an aerosol can of starting fluid (or carb cleaner, WD40, or an unlit propane torch) and spray it around the carb intake boot, around the throttle shaft, and around the boot to the head.
If there is a vacuum leak the engine's speed will change as extra combustible stuff is drawn into the intake.
Likely suspects are poorly sealed carb boots to the air box, head and the carb, cracked carb boots, or a worn throttle shaft bore.
You should also check all the vacuum lines that are coming off the intake manifold for leaks. There is one that goes to the petcock and one that goes to the AIS.
Make sure that the throttle cables are not sticky, too. Open the throttle about a quarter turn and let it gently close a few times. The throttle stop screw should firmly touch the throttle stop. Sticky cables could be the culprit, but the throttle return spring is pretty strong so this is a bit of a stretch. Do this with the engine running. When the throttle has returned, press on the back of the stop screw. The idle should not change.
Give it a shot.
Tom [email protected]
“Neither of the two people in the room paid any attention to the way I came in, although only one of them was dead.”
'How' are words so important they cannot be too often used.”
Sting like a butterfly.
Last edited by Tom Schmitz; 05-13-2015 at 01:35 PM.