I have a 1999 25 Honda (4 stroke) 25 HP on a RIB. It has run very well for several years. This year upon start up it runs very rough (if at all) in idle, sometimes I can shift into gear and runs normal at high speed. I typically add Stabil to the fuel tank (aout 10 gals.) in the fall. The problem, rough idle occured this spring. 10 days ago I took the boat and engine to a Honda dealer. His basic diagnosis was water/dirt in the carbs all E10 related. He removed the the 3 carbs, cleaned them in a heated ultrasonic bath, installed a new water/filter separator. He ran it on his own polished fuel and said, all is well. After the repair and before launching I siphoned the fuel out of the internal RIB fuel tank, added an enzyme treament, and new fuel. Launched the boat and the problem continues. I removed the new filter cartridge and put the fuel in a clear plastic container, ...no water, looks OK to me. I drained the carbs and the problem continues. Any suggestions?
