At my wits end... almost. I could really use some help.
I should start with what's (checking out) "correct".
Headlight, tail light, brake lights all work properly
Rock solid timing (mark to mark w a light), fat blue spark, new points, zero sparking inside the stator when running.
New piston, rings, fresh crosshatch.
Head, intake, exhaust and base gasket, mag-side seal, spark plug (B7hS properly gapped). all new.
Delorto 14.12 with mesh filter
58 jet (have tried from 52-62 with same overall results)
Stock header with (slightly) modified Columbia-Sachs cigar pipe.
NO leaks anywhere, I have DOUSED this thing with carb cleaner as well as soapy water while holding the throttle at the minimum position necessary to keep the bike running without a hiccup.
The bike takes 3-4 kicks with the choke on to get popping, then starts easily holding the throttle 1/3-1/2 open, as long as you hold the throttle open "some" it will stay running, you can allow the RPMs to go down to "almost" an "idle" and keep it running with the throttle.
It runs rough and (on the stand) is slow to rev crisply, will not begin to power the bike.
The next steps (If necessary) replace the clutch-side seal ... seems I might as well rebuild the whole bottom end at this point, even though it seems smooth/quiet when running? The only possible abnormality is I can move the crankshaft about 1mm side to side holding the flywheel.
The only other thing I can find is the replacement piston is about 3mm longer (pin center to skirt) than the stock one, all other dimensions check out.
The bike has 3200 miles on it, and there's evidence the PO had their hands a lot deeper than they should've.
Any gurus have any ideas?