I have a 2003 Johnson 2 stroke that only runs on the top cylinder. I bought this boat as is. I have checked compression and both cyl. are 140psi. I installed new plugs. I used a spark plug gap checker and it jumps 7/16' gap on both cyl. I removed carb. cover and placed my hand over top carb. opening and the engine died. No affect on bottom carb.I squirted fuel in bottom carb. while cracking open throttle a little and still no affect. Both carbs have been rebuilt. I even swapped top carb to bottom with no affect. HELP