Idle Fluctuations in Drive

[Cliff Ruggles]

Blocked idle bypass air holes in the main casting indicate commercially "remanufactured" at some point.  There in may lie some of if not all of the issues and not responding well to larger IFR's and DCR's.

In any case remove the plugs in the bypass air holes in the main casting.  Now measure the bypass air holes in the baseplate.  See if it likes the bypass air as-is. 

I'd also add that going from .038" idle tubes to .0375" is really no change at all in the big scheme of things.

Since the carb may have been "remanufactured" at some point you may also find mods have been made to it in other areas not for the better.  Probably a good idea at this point to measure everything and compare to stock specs......

[Shiny]

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I read some other posts on removing the APT cover/screw.  There seems to be some issues  from us DIYers in breaking the screw and or damaging the baseplate when drilling the broken screw out.  Although the turnability advantage is intriguing, as my part throttle is not an issue I think I will leave that alone for the time being.
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I am one that messed this up.  I had to drill out the APT screw and ended up going sideways.  I unknowingly punctured the baseplate and introduced a vacuum leak I wasn't aware of.  I was happy Cliff had the nice replacement screw, though!  His part was NOT the weakest link...

I would not hesitate to do it again, but I'd use a drill press!  It is not complicated and can be done with a good bit, a drill press, and some care.  Yours might be in better shape and actually yield to some penetrating oil and/or some heat cycling.

As to the bypass air, I struggled to get mine idling well.  When it wasn't flooding, I had an obvious nozzle drip from needing too much throttle blade.  I finally realized it was a Frankencarb with mismatched parts that didn't complete the bypass circuit I thought I had...  I ended up sending the carb off to a pro who added bypass air, discovered & fixed the APT leak, and tuned it for my engine.  The throttle blades now close and it idles off the idle circuit!