I have a 1989 yamaha 2.6 litter 225 excel. A few months ago the motor started surging at WOT, removed the fuel cap did not help, pumped primer bulb and motor picked up rpm's. I replaced the fuel line from the fuel water seperator to the motor, primer bulb, fuelpumps, and spark plugs. The line from the inboard fuel tank to the fuel water seperator was clear - was able to blow into the tank without restriction. Afterwards the motor ran great for about 10 + hours. This weekend boat ran great on the way out at 5600 rpms, started to come back in the boat started surging would not go above 3400 rpms, primer bulb was not hard, pumping primer bulb boat ran much better. Changed fuel water seperator, and checked fuel line conections helped a little. Any help would be appreciated.
check the fuel pump diaphrams again and do a fuel system vacum test. all you did by pumping the primer was bypass the fuel pumps and manually added fuel to the fuel bowls.
once the bowls are filled you can throw the primer in the trash, thats in one and only function in life.
either the pumps are weak or they cannot suck fuel due to an air leak or a restriction.
a good place to start is to bypass the quick connect fitting on the cowl.
a 15 dollar vacum guage some tubing and a t fitting will help.
no tech questions by PM, they wont get answered.
you have to be trusted by the people that you lie to .