I am looking to purchase a 99 kenner with a 90 Mercury engine. We took it out to test drive. It seems to have worked alright at first then would not accelerate above 4,000 unless you babied it up their. I had the shop pull the plugs and the upper plug is dry. The other two lower plugs look ok. The motor would smoke a little upon initial start up. But would have alittle trouble starting after a while. The compression for all three cylinders is ok. Could it just be that it needs the carbs cleaned up? I want to buy the boat but want to make sure that it is just the carbs. Any help would be greatly appreciated.