Ok, I ran the PTR36 today for 2 fuel tanks (10 oz ) 5 on (2500rpm) and 10/15 cooldown.... was on the 3rd tank when it started to run real rough.
and died..... changed battery same  hard to start ...its blowing alot alot black stuff all over the test plane, changed plug, checked timming all ok, changed ignition box (DLE30) still the same thing, was using fresh mixed fuel 1:32 Stihl Ultra.
Hard to start realy hard at 30/40% throttle, runs at 2500 rpm goes to 3500 won't run above or below.
Carb stting where not changed exept on the beginning 1/4 turn rich on both...turned them back no change.
Had to quit my arm hurts to bad from flipping ............................ 
 Any thoughts ?