[MENTION=65307]Sportster-2001-951C-Stock[/MENTION] , those bypass ports, where are these actually located? are these the little TINY holes inside of the carb throat?
Yes, those are the most important passage in the carburetor b/c 90% of the fuel consumed comes from them unless you ride WOT all the time.
The holes are circled in red in this photo. If they're clogged even a tiny bit you will experience hesitation and this leads to detonation due to the lean mixture riding around part throttle. The big main venturi only begins flowing fuel at throttle angles greater than about %50% or more (depending on model, 951 it's about 70% throttle).
So these holes are the problem almost always, look how small they are it doesn't take much, just a little corrosion to cause a restriction and totally throw off the part-throttle mixture calibration. You can manipulate pop pressure all day long and never compensate for one of these being partly restricted.
Anyway, you've got to restore flow through these holes otherwise you're wasting your time.
The green circle is the idle fuel discharge port. The idle mixture screw feeds this one so you can adjust the idle fuel mixture for an easy hot restart and idling around so it doesn't load up on fuel and choke out. Gotta get that balanced, usually idle mixture is pretty good with this screw set to factory spec unless this port is clogged with junk.
Idle mixture won't have much effect on part throttle but having it just a hair on the rich side keeps enough fuel in the crankcase just the same as an accelerator pump gives that initial extra fuel needed the instant the throttle is cracked open and vacuum drops for the 1st split second. Stick to factory setting for idle mixture screw adjustment, it should be very close to perfect.
Just sayin', getting these bypass (off-idle part throttle transition) holes cleaned out makes the difference between success and fail. And I mean clean, as in back to original diameter.