[Kenth]

Originally Posted by srmmmm

I did discover I can close the idle mixture screws all the way and the engine still idles, so the APT must have been "adjusted" and the true possible cause of the remaining issues.

It is not entierly impossible that your engine runs on the off-idle slots when the idle needles are seated, or are they?

Maybe the springs are long enough to stop the needles before they hit bottom and closes off the holes?
Remove the springs and seat the needles, does it still runs?

And, adjusting the APT will do NOTHING for the idle needles position, the idle circuit is a separate stand alone circuit.

FWIW

[srmmmm]

Originally Posted by Kenth

It is not entierly impossible that your engine runs on the off-idle slots when the idle needles are seated, or are they?

Maybe the springs are long enough to stop the needles before they hit bottom and closes off the holes?
Remove the springs and seat the needles, does it still runs?

And, adjusting the APT will do NOTHING for the idle needles position, the idle circuit is a separate stand alone circuit.

FWIW

I'll pull the springs off and try. I do already see the tips of the needles protruding into the barrels right now. But I had thought the height of the power piston was possibly altered by the carb rebuilder to allow more fuel to be available to the idle circuit and transfer slots in anticipation of the cam I was running.

[Kenth]

Originally Posted by srmmmm

I'll pull the springs off and try. I do already see the tips of the needles protruding into the barrels right now. But I had thought the height of the power piston was possibly altered by the carb rebuilder to allow more fuel to be available to the idle circuit and transfer slots in anticipation of the cam I was running.

The square area between jets and rods will always be larger than the square area of the idle tube restrictions, thus it wont matter how you adjust the APT.
As said before, the idle circuit is stand alone circuit.