I did a search on the need for bushings, and there seems to be some disagreement on what is needed in this regard. My carb has a large amount of slack in the shaft, you can rock the shaft around, up and down, fore and aft after you unseat the blades from their bores. If I had to guess, I'd say you could move it about .060-.100 total up and down as seen on one side at the shaft. You can hear everything clacking around when you move it around with the blades open. With it shut off, if you stroke the throttle it will dribble a couple of drops out of the shaft. But I was wondering, with aluminum expanding like it does, don't you want some slack there? In your educated opinions, how much is too much? If its vacuum leaks that are a concern, the PCV is a big one that you just have to tune for. I'd rather have the engine run consistant, than heat up and have the carb get sticky. BTW, the thing runs fantastic right now as it is. I re-epoxied the well plugs and man it runs and stats like a dream. The most responsive 352 Ford there ever was! And it purrs like a limo. Since this carb is a counter replacement 1705 carb with no real resto car value, I am going to graft a 429CJ style auto trans kickdown onto the throttle shaft, I am going to rebush it while I am there I guess, but how tight does it really need to be? Expansion is amazing, in an aluminum head, aluminum block combination, I have had to set the valves at zero lash cold to get .022 hot. Opinions?
It is common knowledge that all Q-jets need to be rebushed. Even bran new ones as this will prevent wear. Every Q-jet expert I have ever talked to or read has stated this. When the throttle is closed there should be no play. The fuel wells also need to be epoxied over. Lots of problems there as well.
I saved this info that I believe was posted by Jon (carbking): >>>The factory design tolerances on the AFB were 0.016~0.022 inches. This is necessary due to the expansion of the large bearing surface area on the AFB. Too tight a clearance will cause binding when the engine is hot. Conversely, the factory tolerances on the Q-Jet are 0.004~0.006 and bushings should be installed at 0.010.<< You can just barely feel 0.002" clearance, but 0.100" is close to 1/8" (0.125") :eek2: , so it's unlikely you have that much!
