Hello all my mate need some help. He has a 2009 290 Sherco. When you start it up all it does is rev its self sky high. Throttle cable fine carbs been removed and clean including jets. We just don't know what's up with it. Hope someone has some ideas.

Thanks

If the throttle slide is snapping back with an audible thunk then I'd be thinking ignition side crank seal or possibly leak at the manifold. Which carb is he running?

Thank you tony27. Its running a dellorto carb. How would you check the seal or a leak at the manifold?

Thanks

When did this problem start?

Again-Can you hear and feel the throttle slide hitting the bottom stop when snapped closed?

You gotta have a heluva air leak to do that much revving.

He's only just got it and seem to start the day after. You can hear the throttle hitting the bottom. How am I going to find this Air leak.

Spray soapy water around the carb etc while it's running & if the revs drop momentarily then you've found your leak

I just experienced they same issue. I put the bike away over the winter and treated the gas with stabil, as I always have.

I started the bike last week and it didn't want to die without the choke. Common issue - I cleaned out the carb (no thanks to Stabil) and put things back together.

Bam, first kick and she was purring. I took off the choke and the bike went from idle to high revs. I adjusted the idle screw and it eventually came down, but wanted to die. I adjusted the idle screw to bring the idle up a bit. It was idling well, then without warning began to rev like crazy!

Also, if it is idling and you hit the throttle, it will stay up on revs for a very long time.

Sound like an air leak somewhere?

Thanks!

Check the o ring on the top of the carb also if it's hard to start could be the base gasket but you should hear it chuffing if it's the base gasket

Hello Everyone. We finally got the the bottom of our Reving problem, after changing both crank shaft seals she is running a real treat. Thank you so much for all the help.

I just experienced they same issue. I put the bike away over the winter and treated the gas with stabil, as I always have.

I started the bike last week and it didn't want to die without the choke. Common issue - I cleaned out the carb (no thanks to Stabil) and put things back together.

Bam, first kick and she was purring. I took off the choke and the bike went from idle to high revs. I adjusted the idle screw and it eventually came down, but wanted to die. I adjusted the idle screw to bring the idle up a bit. It was idling well, then without warning began to rev like crazy!

Also, if it is idling and you hit the throttle, it will stay up on revs for a very long time.

Sound like an air leak somewhere?

Thanks!

Same is happening on my beta

Good call by Tony, and good feedback on the fix. Just another example of my 2-3 year theory on the stock seals, yet normally things do not get that bad overnight!