I have a 86 Mercury 9.9 outboard that has a lack of power after you first start it. It starts fine, it will go about 100 yards like it is running on one cylinder, if you give it too much gas it will stall out, after it seems to warm up it then will open up and run fine. After you shut the engine off for awhile it will do it again. I changed the gas and went to 93 octane, I mixed Sea Foam in the gas, cleaned the fuel filter, and changed the spark plugs. It has been doing this all season and does not seem to be getting worst, it is just annoying.