If its been sitting that long I would warm it up good and check the valve adjustments. I'd bet you'll find that you need to do some adjustments. Just make sure that when you warm it up that you get the oil hot, not just the water temp up. It makes a difference. Then as Denny suggests, do a compression test. You can get a cheap compression tester for less than 20.00 if you look around.
Good Luck
Don
