hi low end set up on the 91fx-run the engine about 10001500 RPMS back out the low end until it starts to run rough-turn it in until you get a real smooth run at that RPMthe low end is set to go-do this only after -you ran up the top end once-then do the top end again after the low end is done - do go richer than you would normaly on the top end adjustment on this engine you need to fly the plane to see the results i have been working with my 91fx to get it to run better for a month and a half i do have mine a long time10 years but about 50 flights -it has never gone dead stick but my problem is i just cannot live with the sound this engine makes in flightI JUST HATE ITbut the power is great