I recently purchased an '05 CRF250R for my son. The bike ran when we looked at it but two weeks later went and picked it up, it wouldn't run once we got it home. Pulled and cleaned the carb and found the float valve stuck closed. Once I started it, it had a rattle in the upper engine, like under the valve cover. Pulled valve clearances and re-shimmed exhaust valves and re-assembled. Rattle is still there. Checked the tensioner on timing chain and it is putting good tension on chain. Any ideas???