Pat,

Just found your post today after posting a similar message on the MVVS site yesterday. My 35cc/2.15 CI has the same problem. Prop is balanced to a gnat's whisker as is the spinner. Engine runs smooth as silk at all RPM's...but carb comes loose every 4 or 5 flights causing engine to go lean and an immediate landing.

Each time I clean the set screws, Loctite them, and allow them to cure overnight. The screws don't back out but the carb still works loose, letting air around the collar seal. Seems to me the screws don't grab the carb mount with enough grip and the combination of vibration along with operating thermal cyclces is causing the carb to work loose. Engine almost sounds like it is running low on fuel when this happens.

Otherwise my 35cc starts and runs OK.

I have a couple of ideas for a fix but hope one of the experts has some insight to share.