I had nothing to do on the farm today so I took EDs advise and put the 91fx out of the little cap into a plane that was good I have about 12 planes at the farm but I chose the easy one..HANGAR 9 super stick 60 had it for about 3 years kids use it as a trainer...61FX for power so could change motor to 91 in less then 5 min...flew the plane once to make sure everthing was goodplane has more then 200 flights on it and 61 has never dead stick or given any problems......has std fuel tank with 3 line setup....after flight changed to 91FX...13x6ms prop..new oring for carb..all other gaskits new..head removed no peeling on cylinder wall...os#8 glowplug..omega 15 fuel..motor mounted upright so could use stock 91 muffler with bafful..ran plane on ground for one tank.ran good but not as good as the 61..one or two clicks of the needle make diff.to it but the 91 you could move it a half a turn with little diff.....set high speed needle to very rich seting as OS said to do....running not to bad so took off...very rich good smoke trail..this 91 sure polls this plane a lot faster then the 61.. IM sure if you let it the 91 would fly it to pieces plane seem to fly great good smoke trail then in about 3 min. the motor started to loss power ( still had good smoke trail) and run very rough landed plane still running had to turn needle valve back almost 3/4 turn to get it to run as good as begining***plane ran good on ground so took off again good smoke trail but maybe less..plane fllew good for about 2 min. then motor stoped dead stick##(still had smoke trail) which is no big deal with this plane ase a blind man could almost land it###filled tank had to open needle valve to get motor to start tried two more flights all ending in dead stick## maby needle valve was bad so changed to commeplet new back plate assbly I purchased last week##motor still ran the same..sometimes not even lasting 2min. in the air but RUNNING GOOD ON THE GROUND###* 8 flights all ended in dead stick unless you landed and adju...needle sometimes twice####motor would only run super rich in the air if you lean it down motor would not last 30 sec. in the air but run fine on the ground###please remeber that this plane flys great with the 61FX and ther is no air bubbles in line from needle to carb....I put the 61 back on the plane and had a great 15min flight landed it and put it back in the barn before the kids come I have 6 46FXs 2 50sx and 3 61fxs and all these OS motors have never given any proplems????????? I will try tomor to run the 91fx out of the sea fury but it dosent look good###this 91 was doing the same thing in the midwest little CAP and a differant plane did not help###OS STILL CLAIMS THEY DO NOT HAVE PROPLEM WITH 91FX......IVE DONE everthing they said##needle valve change..stock muffler...13x6 prop...fuel tank within 1/2 inc. of centerline...larg fuel line..lone break in must have at lest 2 gallons of fuel throught it by know########and the motor is stillno good....this motor is out of warrinty but the other one is still good so willsend that one back####....LOTS OF PEOPLE ON THIS SITE WITH NEARLY THE SAME PROPLEM HAS ANYONE BEEN ABLE TO FIX OS91FX OR IS IT JUST A GOOD PAPER WEIGHT ?????? or should i look for a SAITO 100 for my chipmunk it would be my first 4 stroke :drowning: