I recently picked up an XS 400 as a first bike. I have gotten it certified and on the road but I am having a problem with throttle control. It starts fine, but as it warms up, it begins to race. At first the RPMs will just stay up at 3000 to 4000 rpm when you crack open the throttle. When it is fully warmed up the rpm will climb to 4000 or 5000 without touching anything. I have checked for air leaks and mounted the carb collars with gasket sealer,m but I still have the problem. Any ideas?