I have a '80 Kawasaki Invader 440 cc I bought from a garage sale for $100. When I bought it, I was told that it sputtered but would not fire. I discovered it to be a hole in the left hand (from driver's seat) piston. When I rebuilt the engine, I noticed that that piston had been replaced already, as the right hand side was still original. The new piston looked as if it had barely been run, yet still had a sizeable hole burned through it. Now I have rebuilt the top end on both sides, but still I cannot get acceptable results. When the engine runs, it runs lean and stalls with the choke off, and will not idle with the choke on. When it does run, it runs very well and will even pull the skis off the ground! Other days, it will start and slowly die out as if running out of fuel. Does this sound like a simple carburetion problem or could this be something even more troublesome? If anyone has any experience tuning these carbs (Mikuni 36mm), I could benefit from a few words of advice! No one in my area will touch a sled that old!