i recently bought a boat with a 90 hp chrysler outboard on it, found out that the number 3 cylinder piston rings had broke and damaged the head and piston. my friend found me another 90 hp chrysler outboard that was running spring 2012 then was stored so we changed it over it will idle very lumpy then backs fires through the exhaust then cuts out have tried static timing it and also found nomber 2 carb idle jet only out by half turn so have set that to 1 and 1/4 turns out still not running any ideas