ORIGINAL: bob27s
here is your problem........
Engine and Muffler - OS55 with w/ bison pitts muffler
prop: 13x8
If this is the OS55AX 2c engine , you want to use a 10x7 or 10x8 prop !!!!!
13x8 is WAY too big. It is a 55, not a 95
Read similar posts on the matter.
That will get you at least on the right track.
sorry about the confusion, I am actually using a 13x6 prop, i checked in the os manual and it says you can use a 13x6 prop on the engine, so i think the prop may not be the issues......please continue posting some solutions or tips! thank you!