Im on my second tower 75 and have had the same problem on both.i sealed the back plate with a gray type sealant ,i also sealed the fuel nipple going into the carb.make sure the carb is down tight on the motor and move the high speed needle to the carb.i also placed a small piece of fuel tubing over the high speed needle so no air could leak in.before this i was doing what you did.now it runs great except for a rich mid range but thats what the first one did to.the first 75 became my favorite because it was the one i could count on to be trouble free every time i took it out,until it ate the front bearing.i sent it back in under warranty and got a new one,my second one,but this time i knew what to do to fix the problems.i have it on a beat up harrier 46 with a half a pound of extra weight in repaired balsa and covering but it goes vertical like a rocket.hope this helps