OS 91FS
 

Hi
My first post on this site,I have a problem with my Os91FS II,its mounted in a Big Stick 60,when I go inverted it riches up,
upright is OK, also if I do a 4 point roll it does the same thing, a normal roll is OK.
Any thoughts?
Thanks
Yay in OZ

RE: OS 91FS
 

Hi!
Tank to hight at inverted!
Mount the engine on it's side! And check the tank hight!

RE: OS 91FS
 

Raise the tank it is mounted too low.  Also check muffler pressure the pressure tap may be plugged.  Consider a uniflow setup as this helps especially with leaning out as the fuel burns off.

RE: OS 91FS
 

They told you what to do but not how. You need to mount the tank so that the centerline of the tank is even with the throttle barrel of the carb. With a lot of four strokes, that is difficult to do since a lot of planes are designed for two strokes where the carb is above the crank line. Like he said, mount the engine in its side will take care of a lot of the problem. When all else fails, you can use a Perry pump to provide constant fuel pressure. I had to do this on my EZ P-51 racer.