[HEI451]

Why do you only want to slightly reduce the air leak with a solid bushing, when you can virtually eliminate it with a different "filling" material?

I do this all the time, and have one to do this coming weekend. I learned this when I worked for Holley in the race carb department,mbut use it on every carb I do, especially Q-Jets.

A solid bushing only takes some of the air leak away, because it still requires a clearance so the throttle shaft doesn't bind when the carb is retightened back to the manifold. The reason for the clearnace, binding, or, not causing it.

The right way to bush a throttle shaft is with TEFLON. On most Q-Jet's, the actual load surface in the base plate is not large, but, at the throttle bore edges, not all the way to the outside edge of the shaft bore. Most Q's have a .030 larger bore on the base plate from that load carry area, to the outside of the base plate. This .030 area is perfect to use a piece of .014/.015 teflon sheet (available from most better hobby stores), cut into the bushing. Yes, in theory, there is NO clearance, but, the teflon doesn't stick, nor bind the shaft, so, maximum sealing, no binding, and no outrageous machining work needed.

Q-Jet's are notorious for having binding issues when the front hold down bolts are usually way, way over tightened, literally bending the carb, top, body and base plate.

Also, when you refit the throttle plates after bushing, please, use a stainless steel button head Allen screw, Lock-Tite in place, and stake the threaded end into the shaft, to make absolutely syre they are tight, mand stay that way. To "qualify" the throttle plates in their bores, close the shaft and plates all the way against the throttle bores in the base plate, then, tighten the plate screws. When done, there should be easy movelemnt of the plates off the bore sides, without the plates sticking in the bores. Don't be surprized if you have to go over the qualifying operation a few times, it is extremely important to get it right.

Please note, on a very few Q-Jet's, and all the other carbs that don't have the bigger cut in the throttle shaft bores, I chuck the base plate into a drill vise, shaft bore up and down, then, align the bore with a straight shaft into the drill press chuck, then, remove the shaft and install the correct drill bit to create the teflon bore, and cut the bore down a bit, but, NOT all the way into the throttle plate side of the throttle bore. This way, I create a step at the inner edge of the shaft bore, to hold the teflon from migrating into the throttle bore. The stuff that hangs off the ends of the shafts keeps the teflon in place on the outer edges of the shaft bores.