I have a Grizzly 660, 300 hours, 10000 km(6200miles) 2005 mod with dyno jet and K&N filter on. Other wise it is stock standard.
On a level road it normally go 102 km/h but now it only get up to 92 km/h.
I have cleaned the carb and air filter, checked the valve clearence, changed oil and spark plug.
No improvement.
In low range it normally hit the rev limeter at 65 km/h and now it is 56km/h.
How do I know if the clutch, belt or pulley is ok?

 

I would say either your belt is worn or you have mud in your clutch. Both of those items will decrease your top speed.

 

I have opened the belt/clutch cover. The belt look fine and i can see no mud but when i put it in neutral and rev it a bit the variable pully push the belt out but only to about 10 mm (3/8) from the outside of the pully. Is this far enougth? Is the clutch on the front or the rear pulley?
Thanks for your help.

 

I would replace the belt and regrease the primary clutch. With that many miles on it I really think it will help

 

I agree thats a lot of miles on one belt.

 

Someone correct me if I am wrong, as most of my experience is with snowmobiles.

Both "pullies" are clutches. You have a primary clutch (mounted on the engine) and a secondary clutch (mounted on the transmission). At full engagement (high rpms), the belt should be fully to the outside of the primary clutch. If it isn't, you will have a lower top end speed. The cause can be either in the clutches or the belt. As they said above, in your case it sounds like a worn belt. As a belt wears, it gets narrower, and will not fully attain top speed.

 

Thanks for the advice. I will update you all.