Hi, I have a mercury 100hp 88 outboard, i have some issues with the engine fluctuating rpm. I was thinking the gas line had air in it or a sticky carb. I added an additive to the gas and i think it worked because it seemed to run without fluctuating. The issue now (can be related) is that it won't always start or starts when the trim is up. Ok at higher RPM but dies when i throttle down or lower the trim. I wanted to add that it seems to smoke more and noticed some gass in the water when running. Is it a cylinder not working - carb or is it something else? Thanks