I run my YS 140 at full throttle, the airplane is flying fine, then the engine sounds like its going to quit for a second, then goes back to full throttle. It does it quite often but never quits, justs stops like its going to quit, and then goes back to full throttle. It did it today below full thorttle, but usually it does it at full thorttle. What causes this??? I might try a different plug? I use an APC 18x6, YS Blend 25% from S&W fuel. YS 140FZ. The DZ didnt do this for me. Just this one.
Ryan

Maybe just too lean, but hard to say from your description of the problem . Try putting all new plumbing from tank to engine.

do you need to have the OS Type F plug?? I just use the regular OS #8 plug. Also I dont use a muffler on my YS FZ. The muffler on this YS is the stock one, and the muffler kept on vibrating off, so I just have the threaded part on, but I guess that wouldnt do nothing to hurt it. Im going to try new filters to

Get rid of the plug. That's the problem.

OS TYPE F OR YS #4 only!