I was given a Kubota G5200 by my uncle last week. It had been sitting outside exposed to the weather. He said he had been told it needed a new head gasket. I got one and replaced it. I did not change the oil as I wanted to make sure I could get it running before putting in new fluids. I did put new coolant in the radiator though. Once I turned the ignition, it started right up. I rode around on the tractor thinking that the light gray/blue exhaust smoke would stop after a bit, but it never did and I rode arround for about 6 or 7 minutes. Power seemed to be fine when riding arround. What could be causing this?