Beta 2018 250 factory. My son fell off it was revving madly but he had landed on kill switch so couldn't cut off straight away.  We let bike cool kickstart was free so not seized.  I removed kill switch at connector ant there appears to be a spark.  It does eventually start on choke and run normal but wont keep running.  I was wondering if carb is blocked with all the vibrations of high revs or he may have knocked something electric wise.  I haven't checked woodruff key as only have a puller for rev3 not evo.

 

Any help appreciated

Woodruff key is still your best bet. Nothing should vibrate apart no matter how high you rev. You could pull the reed block to make sure they weren’t damaged but it’s unlikely as when the bike is at high rpm the reeds just sit full open so they aren’t really stressed. 

Edited April 16, 20197 yr by dan williams

I would pull off the exhaust header and take a quick look to see if the rings are now stuck. You will know by how the piston looks.

The float isn’t stuck down? The little support pin can slip sideways when on the side revving it’s tits off. Ask me how I know??

Lightly nip the pin where it sits in the castings with side cut pliers. It won’t move again then. Float issues banished. 

Edited April 17, 20197 yr by pindie

After a similar experience.   I had the rubber boot between the carb and intake come loose (look closely, it can look like it's still connected, but it's not).  It will become super lean, as I had a huge air leak.  I could get it started with the choke on, but it would not stay running once the choke was off.

 

Edited April 17, 20197 yr by markbxr400

Thanks for all the ideas I will check today or tomoz and post findings hopefully something simple like this

pulled Woodruff key and replaced as matter of course , cleaned carb but not checked reed valves as yet.

thanks for the help so far