Flew the Sea Fury and was able to get back to about 6200 rpm before it just got too hot to keep foolin around with the engine. So. on a hot, humid day (93 degrees @ 85 % humidity) I got back most of what I lost by tweeking the HS needle. I really didn't want to lean it much because big war birds don't glide too well. So just work on your needle setting. Once you get where you want it to run, leave it alone.
AMSOIL is 100% syn. and really does a great job after your engine is broken in on 2-3 gallons of 32-1 petrolieum 2cyc. oil. I get mine from a guy that shows up at a swap meet I go to every March. Look them up on the net, I am sure they have distribution almost everywhere. You might try a motorcycle shop too.
One of the best benefits from the stack on my G-62 is now the btm. of the plane is clean and not covered in green oil slime. Plus I can now get an easy 15 min. flight from a 24 oz. tank with 5 min. of fuel to spare. Before I had about 10 min. and then it was drop the gear, flaps and land. Forgot to refuel about 2 weeks ago and got another 5 min. out of the tank before dead stick time. Was lucky that she quit up high so I could get her down w/o a problem. Needed a new pair of shorts though.
Almost forgot, I am running a Bennett muffler so no back pressure there. I have a friend who has a stock G-62 muffler with 3 3/8" tubes welded into the bottom of the muffler w/ the baffels hammered shut and welded up. Runs great and sounds better. May try that next year. Not going to fool around with my set-up anymore this year, just fly it.
Good luck,
Lou