Randy,
This past weekend we had a contest and I got some strange engine perfoamance. I"ve been running a Stalker 66RE in my big Eather Firecracker. I run Powermaster YS Saito 20/20 and runs have been just about perfect for the past 3 years. The contest weather was hotter than anything I've flown in and on both officials the run was normal until the square eights when the engine leaned a bit and stayed there. Wasn't unmanagable but was noticable. Total run time was slightly longer as to be expected. Sounds like slight overheating to me. Would adding another head shim be the proper fix during really hot weather or just a reduction in nitro?
Alan
Alan
In hot weather you have to run the motors harder and leaner to do the same job.
And when you add a head shim you will have to lean the needle to get back where you were,not the way to go most times the "best" way to do this in heat is to either up the pitch of the prop, which is the recomended way.
I do this by having the same prop in .2 tenth or 1\4 more pitch, When you up the pitch the needle goes back a little richer setting, this way it runs cooler, and almost exactly where it is in a little cooler weather.
the other way is to add more nitro, and back the needle out to a richer setting, but..since you are already at 20% I would just use a little more pitch.
Many people do both, as this adjust for the loss of oxygen that the motor sees, and for loss of lift in hot humid air,
this also works for FAI fueled engines, run about 1\4 more pitch in hot weather and\or use about 2 to 3% nitro.
At this years NATs, I just went from 5% to 7.5% when it got hotter, then back to the 5% when it got cooler mid week. Others there just went from 10% back to 7.5 when the weather cooled, and at least 2 people that I know of just went from a 4.25 up to a 4.5 pitch prop of identical type.
Randy