honda cr250r

I have an 01 CR250 and the kickstart slops down and vibrates on the pipe. What is the cause of that?

me and a buddy was out riding trails that are thick with sand and are also some decent dirt trails. I was riding a 98 CR250R Power Band. Granted I was giving it hell. Usually we would stop about every 30 minutes to give the bikes a rest because it's hell on them in the sand, plus it is tough...