os 91 fx knock/ping
 

first of all THANKS!! WHAT A COOL SERVICE!!
OK I have one of the 91 fx powerhouses and it give my four star 60 unlimited vertical, but IT KNOCKS at lower throttle positions 1/4 to 1/3 . i have stopped flying this plane because i,m afraid to damage the motor. reliable experienced assistance was available for break in and setting the needle valve and low settings . we tried richening up the low setting but this caused it to load up and die. DEAD stick low over the pond was "fun"! i was careful to seal the needle valve assembly and fuel lines etc. and it runs fine except for the knock in my cruise rpm area, any sugestions. DSIP

os 91 fx knock/ping
 

David,

Many engines .91-sized and larger make a 'knocking' sound at low- to medium-throttle settings. We've investigated a lot of engines that make this sound, and could find nothing physical that could make the sound, and found no engines damaged as a result of it. We've concluded that it's an exhaust note, and can change with fuel type, exhaust system, propeller, and so on. Usually, it's just something to live with.