It happens when i rev the engine full and im afraid to over tight the bolt in case i ring it. please any advise would greatly be appreciated thanks.

See this thread here in this forum for information.
http://www.rcuniverse.com/showthread...380&forumid=22

EXCAP2322

Your engine may be running a little too lean causing it to backfire which can spin the prop off. Try richening up the mixture.

How about letting a fellow club member or flier try to tighten it up. You might be surprised at how tight you can tighten them up.

Crank it down as hard as it will go. Very rarely do they break when tightening. Also be sure to re-tighten wood props every now and then as the wood hub dries and shrinks a little, loosening the nut.

Jason,

The best prop wrench is a box wrench that fits your prop nut. Usually, it'll be about a 6-inch wrench. Grab the prop in one fist and the wrench in the other, and tighten 'er down. You can go just short of crushing the prop under the prop nut on a wood prop, and about as tight as you can get it on a composite prop.

If you don't have a box wrench, use a 6" adjustable wrench.

bax

My OS 46FX started doing this recently along with some other weird things. And in order to get it to run OK I had to set the needle valve and idle abnormally. I traced the problem back to a bad glow plug. New plug, back to smooth, reliable operation.

Try a new plug and see if that solves it.

I replace the prop washer with a Higley lock nut, followed by the prop nut, in my two strokes. Works superb

make sure yer not screwing the prop on. It must be reemed to fit on the shaft.
d

I bet dollars to doughnuts you've got a plastic spinner. Get rid of that thing, and get a Higley heavy hub or light hub and your troubles are over.

Just by the fact you get it started without spinning the prop off says something. I agree that the engine may be a tad lean.