Help please...I rode a trial last weekend and on the second lap at section 4 small up hill section,no problem,got half way up and the bike started to back fire,then rev ,them backfire again before stopping and not starting since.The bike had been running like a dream prior to this happening. I've cleaned plug,air filter and had the carb off and cleaned jets and cheched the reed valve,they all seen ok. Has any body had the same problem or know what this problem could be.

Thanks.

The flywheel may have come loose or the Woodruff key may have broken. The woodruff Key is 3x3.7x9.7 in size if you need a new one. The Beta part number is 12.46000 but you can buy a replacement from most bike shops.

Exactly the same thing happened to me a couple of weeks ago (see here). Sheared Woodruff key. Pretty easy to sort - flywheel off, extract the shrapnel that used to be the old key, put new key in and reassemble. If you're unlucky (like me), the bottom half of the old key might still be in the crankshaft in which case you'll have to remove the stator (remember to mark the timing position) and carefully prise it out.

Edited February 15, 200620 yr by neonsurge

Thanks for the advice,it was the woodruff key,Stevens trial are sending one today should be here tomorrow...