1992 Yamaha 150 hp 2 stroke engine won't get above 4,000 rpm. Engine compression good at all cylinders, primer bulb new, fuel filters and seperaters new/good, fuel pump diaphragms not broken but not sure if the pumps/diaphrams are weak and they have never been changed, gas doesn't appear to have water, hull vent open as gas came out when filling tank, new spark plugs, ran great when first put in water in May but hadn't been run for 1.5 months when max 4,000 rpm found even at full throttle when we can usually run to 5,000 rpm and plane off fine with 4 adults onboard. Could only get to 3700 rpm with 3 adults onboard but tides and wind could have been the difference here, starts immediately and idles well, a little rough when running at low speed/idle. Any ideas or suggestions on where to go from here?