Dar,
Thanks for the reply,
The reason I'm running an A3 is because that's what the manual for the engine says to use. The reason I use 15% is because for some silly reason it's the lowest % nitro you can get around here. If a cooler plug will get me better performance,or less wear and tear on the engine,I will give it a shot. But I have been running with no issues for a full flying season and several flights this year......so if I have been running too hot,the damage may be done already.
As for the exhaust tube.....when I first put it on,I checked the rpms. Seems like it had no effect,or very very minor,on the O.S. On my Thunder Tiger Pro .46 the tube is longer,and it increased the power noticeably. Seems like the rpms increased by 1,000 or 2,000. I richened it to keep it from overheating. It has been going strong for a few seasons running the same fuel and plug.
Up until now,I haven't ever had any engine troubles. The way I have always tuned them is to lean it out at full throttle until I get max rpms(judging by ear),then back it off until I hear a slight drop in rpms. Then I generally don't have to change it much after that unless there's a big temperature difference from one flight to the next.
I think what I need to do is take the engine apart and clean it,and check the fuel lines....general maintenance. If I don't find anything,I'll just have to try some of these suggestions.
thanks,
Jeff