I have an '02 WR426. The bike has been sitting for almost 2 years. I drained the gas, changed the oil and did the usual service. After considerable effort, I finally got it to start. It was backfiring a little, but seemed to run better as it warmed up. After running it for 10-15 minutes (mainly at idle and low speed) coolant started running out of the drain hose underneath the bike. As soon as I noticed it I immediately shut the bike off. What does this mean?