The Stovebolt Site Forums The Shop Area Engine Shop Changing idle rpm’s

Make certain your throttle linkage spring is good and the linkage is free moving. With a Carter carburetor, it won't take much resistance to mess things a bit and it sounds like something is keeping your carburetor from settling correctly on the throttle stop. It is worth mentioning the Rochester had a strong spring inside which pushed the throttle linkage back as far as it could go and the Carter is built differently. For one comparison, the Carter accelerator diaphragm works "backwards" from the old Rochester pump type and for another comparison the internal spring isn't as stiff. With the Carter, there should be one spring on the diaphragm rod which connects between the bottom casting piece and a sort of C clip about 3/4 of the way up the rod. The pump lifter sits on top of that C clip (remember it pulls up on the diaphragm to squirt gas). Straight on top of this sits the metering rod arm, spring and metering rod and on top of that you'll have one or two springs (depending on the age of the carburetor and how it was designed) and another C type clip at the top. Image of this is attached for you. In the Rochester a strong spring beneath the accelerator pump sits and it will push the pump up smartly. Good luck.