ORIGINAL: Pull Up Now!
My first observations are that the transition from low to high rpm is ok, but when closing the throttle, even gently, the engine quits. Also, it takes an electric starter to get it goingdoesn't want to start by hand flipping like a 2 stroke would. this is after choking with evidence of gas wetness after having done so. Any ideas?
From my 180 conversion a couple things are possible:-
Idle speed too low. Sudden shut-down (sudden closing of the trottle) will work if you are at say ~1800RPM or more idle, but will cut if you set the idle as slow as it will go, say 1400RPM.
Carb without check valve. I'm not sure here, it definitely makes a diffence on 2 strokes, but I can't be sure what exactly what occurs with 4 strokes! My SPE26 had a better/cleaner shut-down in the air with a carb that had a check valve.