ORIGINAL: R-Duhb
<span style=''font-size: larger''>Well it's a year later and I've switched to 5% fuel. The engine will still knock if I lean it out too much, but I thought I had found a rich needle setting that eliminated the knock at full throttle and gave me decent RPM output (8400-9000). So far I've run about 3 tanks thru it. Thought I had it running pretty sweet. The low to high throttle transition (after it warms up) is extremely smooth with no hesitation. However, I'm still having a problem. As the run time increases (along with temp) the knock returns as I increase to full throttle. Of course I richen it up, but I sacrafice lots of power and frankly the engine sounds like crap. I really doubt it would fly well at this setting. Should I expect this to improve as I continue with break-in? Also, is there a rule of thumb for setting the air bleed screw? At one point when I thought I had it running great, I pointed the nose up which caused the RPMs to increase, and guess what....it started knocking. I'll have to adjust the air-bleed screw to fix this, but one problem at a time.
Thanks!!!</span>
Your engine is still in the break-in phase of operation. While OS is known for producing engines that break-in quickly most of the time, occasionally there may be one that slips through that needs additional TLC.
Your 11x7 prop is a bit too much load for a new FS-40. I would drop back to an 11x6, or less (11x5) for a gallon or two of fuel. When tuned appropriately rich during break-in it is not uncommon for an engine to run a bit raggedy and to produce less than optimum power. Be patient. Your OS FS-40 will run great when the fits all fall into place.
Ed Cregger