Mr-413bt, I don't think you said how much fuel you have through your engine but... If needles are set correctly you may have a bearing acting up. I had an engine one time that acted similar to yours and the bearing wasn't loose like they get when worn out it just didn't spin good.

When we were starting out racing nitro we killed the engine by plugging the stinger, we went through alot more plugs then. Grizz maybe try some differnt brand plugs.

Rex