RE: Jett 50 problem
Wingspam:
You sure have something screwed up here. Being a long time lover of the Jet engines, I have never seen their equal with respects to throttle transition, and solid idle. Gotta almost beat mine to make them stop. If you have checked your fuel system and have the needle nut tight, get your torque wrench out. Don't have one, woops, you can not survive with out a decent torque wrench. Buy one. I know someone will chime in here and say they have been in the hobby since JC, and never owned one. I had the same attitude for years until I stripped a head bolt on my beloved 35.
One day after a club race I wanted to change a plug cause things did not "sound right". Kept turning the plug wrench and nothing was happening. The insert button was turning like it was designed to. Nice and smoothly. Had to take things apart to get the sleeve back into place. These engines are that well machined, like a watch, a rollex at that.
Take your head and muffler off, and check your sleeve. Bet its off a little, and that is all it takes to goof things up. Get the sides equal and carefully torque it down in the intended pattern. Both my 50's and 60's need their heads torqued about every 3-4 runs, minimum. Be sure to check the carb and see if it is pushed into the "O" ring properly. Check the rear case O ring for any damage, any small cuts etc., get a new one.
Both Bob's 27 and Dub have instructed me in the past to move the needle valve from the engine case to the airframe when I was having a problem with a 60. It worked, no more bubbles.
If the above has failed, box that engine up and send it back to Dub Jett. He will get her running rignt at a very reasonable price. His service has got to be the best and most reasonable in the world. For what its worth, I run 15% Power Master fuel with a extra 1 oz of quality castor so I can also use it in my 4 stroke YS 63, 90, 110. The Jett engines seem to like this a lot. I do what ever these little guys seem to like, a happy engine is a fast engine. ENJOY