Not telling anyone what to do, just letting you know what happened to me and what I did. I have a OS40FP Muggleton modifiied, Hemi head etc. in my Nobler. When I first started flying it. It was very inconsistant and I couldn't figure it out. Also I noticed that after a flight if I touched the plastic spinner aluminum backplate it was so hot it would burn you. So thinking it was a cooling problem I opened the intake on the cowl. Still the same, so I opened the exit holes another 50%. Still the same. So I went from 22% oil to 24% oil. Still the same and the spinner backplate was still way hot and the runs were not getting any better and it even ran away a few times. I finally got to thinking about the tongue muffler I was running. I don't know where I got it but it's a nice lightweight unit that looks good. I opened up all the holes another .005 and took it out for another flight. Will wonders never seize, a solid 4 stroke through out the pattern which allowed me to lean the needle out a little more for some increased power. After many flights now and each is the same as the last, the problem has gone away. It was frustrating and I was upset. But Finally it all game together. It could of been any one of the above and after drilling out the muffler I could not tell any difference in the noise level. Again, not telling everyone to drill their muffler, just letting you know what worked for me. I was used to using plastic clunk tanks successfully on my profiles so of course I blamed the problem on the new metal tank.....WRONG......Grins