Qjet secondary throttle shaft bushings

[Captive8]

I haven't replaced any secondary throttle shaft bushings for awhile,  but the last set I did, ran into a minor problem. After inserting the bushings, the ID of the bushings "shrunk" some, to the point where I could not start the shaft through either one...too tight.

I didn't have a reamer, so I used the pilot section of the bit to open the IDs back up. But I don't think that was ideal because it can be difficult to control the amount of material removed vs. a reamer.

Anybody else have this problem? Seems like the bit isn't sized just right and there might be a bit more than .001" interference fit. Do I just get the proper size reamer and forget about it...?

[Cliff Ruggles]

I do NOT recommend installing bushings on the secondary side of the carb.  The huge throttle plates need a little "wiggle room" when they close so they can fully seat in the bores and allow a minimum of air to pass by them.

I've seen so many baseplates rendered ineffective from folks installing bushings I can't understand why they would want to?  When a troubled carb comes in here I made a reamer to gently open up the bushings that were installed to provide enough clearance so the throttle plates can be indexed and centered to completely close when they are at rest.

In any case in all the years I've been doing this I've never seen any secondary shafts or bores in the throttle plate worn enough to warrant bushing installation.  Not saying there aren't any out there, but I've just never seen any here......

[Captive8]

This was a first for me seeing an actual vacuum leak at the pass side of the sec. shaft. This carb is on a buddy's car and I'd already been completely thru the it. I went over to his place to install, and it was idling rough at start up with the vacuum gage pretty unstable. Started to look for a leak and found this. The one time I had previously done sec bushings was so long ago, I've forgotten the circumstances.

I'll get a reamer...thank you.

[Cliff Ruggles]

It's not uncommon to find a secondary shaft slightly twisted or bent.  Take the time to make sure that both throttle plates are FULLY seated in the bores with a MINIMUM of light showing.  Failure to do this during the rebuild can and will come up with poor results once the carb is placed in service. 

Two days ago I had a "walk-in" to the shop for a heli-coil.  He brought the entire carb so I had to strip it all the way down to do the heli-coil.  Since I ended up doing the assembly I checked everything and found that the passengers side secondary throttle plates was open with a LOT f light showing around it while the other side was fully seated.  I spent about ten minutes twisting the shaft back in place and told the owner that it never could have worked well like that.

He commented that it's never idled well and not sensitive to adjustments with the idle mixture screws even after having it completely rebuilt and restored about 10 years ago.....FWIW...