So a good friend asked me to check out his 4 wheeler and see what was wrong with it. Had the engine rebuilt several years ago and when it came back it didn't run right. Due to problems with the repair shop they got their money back and just parted ways. Anyway he asked me to take a look at it and see if I could figure it out and I am now stumped.

I put a plug and battery in it and it fired up, drove it and very lacking in power. I know the gas is probably a little old but it's running exactly as he said it did when I put the gas in. At first I thought the cam might have been installed retard so I checked that and it was good. Pulled the spark plug and it's a little black but nothing major. Checked the valve clearance and it is good. So where do I go from here, I know I should probable check the compression. Does any of these symptoms sound like anything else, maybe a clutch dragging or something.

Thanks for the help.