Troy.

I hate to but into a thread but my 140-sport seems to have some of these symptoms too.

Sometimes it will appear to coast to a stop and sometimes it will stop rather abruptly too. There is air bubbles in the fuel line from the regulator to carb line and because the motor is inverted the clyinder head and valve cover are wet with fuel from carb I think.
I too am getting rather perplexed with the motor , and, where I fly here in the UK no-one else has a YS so can't help with tuning it either.
It has good rapid transition from idle to full power and is taching at 8700 on a 17x6 apc prop and 20% MT Yamada fuel.
The idle needle is almost all the way out and yet the idle is rich and will choke up after 45 sec to 1 min.

Any light to shed on it !!!