I need help with my engine , it does not like nitro i run 5% in it flys fine but wont drop back to idle for agers sits there barking at me and is very hard to tune does not peak before going lean have been trying different top and bottom end tuning with no result oil is also black coming out exhaust this is a new motor with about 20 flights , pulled it down today every thing seems ok inside.i have two other planes and none of them give me any problems
please help with some tips please.