I have a 2003 25hp merc electric start 2-stroke, I haven't been using it for awhile but been giving me problems ever since. I replaced spark plugs, fuel filter, gear lube, carb cleaned out, adjusted timing and check fuel lines and everything went great. Plm is motor start right up but little rough and giving it power off it go. Soon it reach 3500 RPM then it bog down and kwit! I replaced impeller peeing went great. Start up again then try again up to 3500 RPM then stalling begin to run very rough. What's up with this motor?? This motor has about 500 hours on it.