I have a 98 Craftsman that had a carb problem when I got it, The needle didn't seat and filled the crankcase with gas. Anyway, I fixed that and changed the oil and it ran fine for the last 2 weeks. Start it up and it did not smoke at all. Instantly starts! Today, I had a guy coming to look and buy. I started it and let it run to charge the battery. It ran for 15 minutes and I got on it to move it up an incline in the yard. As soon as it started to move up the bank, it started to smoke. I stopped and backed it down, it stopped. Wait a few and it did the same thing! Turned it off, let it sit a few and checked the oil level to see if it was filling with gas again. Oil was slightly below the full mark and clean and no gas odor. I told the guy it was not running right and he bought it anyway. Could it be the beginning of a bad head gasket? I know the Briggs OHV are known for this problem. PLug is not oil soaked. Any ideas? I am wondering out of curiosity as to what it may be?