25 hp outboard problem

[Doug Lisenby]

I have a 1998 25hp 2 stroke Yamaha outboard. It cranks easily, runs good on throttle and idle. From mid throttle to wide open, it surges. Have checked compression, changed coils on back of engine, changed power pack, replaced all fuel lines, rebuilt carburators and fuel pump. Still surging. Any suggestions?

 

[john22empire]

Could be a shot in the dark but you could be sucking air from your fuel line or tank.. I have a Mariner that was doing the same thing. I did everything you talked about, and it still did it. Would only run back on choke once it total lost the prime..

 

[guyjg]

replaced all fuel lines,

Every piece of fuel line on the boat? Run it on a separate tank attached directly to the fuel pump. If it stops the problem you know where to look...from the pump back to the tank.