I have an 89 or 90 Yamaha Pro 50 which has been bullet proof until this year. I loved how this motor pushed my boat but earlier this year, it started to run really rough. The motor starts and idles alright. It has always idled a little rough but the problems is at full throttle. When I start upping the throttle, nothing really happens. It tops out at about 3 mph and 2500 rpm. It sounds rough. I have tried cleaning the carbs, replacing the fuel pump new fuel lines, fuel tank and spark plugs. All three of the plugs have spark but they seemed to get covered with oil so maybe it is running too rich with 2 cycle oil?
When this first started to happen, it would run rough for a couple minutes. Then it would pick up until it got to full throttle. After that, It never would get to full throttle. I was thinking that it was a head gasket but I put the leak down tester to each cylinder and they were around 40%. Not great but it should run better that it does at that compression. I'm not sure where to go from here. Any help would be appreciated.
When this first started to happen, it would run rough for a couple minutes. Then it would pick up until it got to full throttle. After that, It never would get to full throttle. I was thinking that it was a head gasket but I put the leak down tester to each cylinder and they were around 40%. Not great but it should run better that it does at that compression. I'm not sure where to go from here. Any help would be appreciated.