1981 mercury 85 horse

[nshirley1022]

i just bought a 1981 mercury 85 hp it starts up great but after about 10 to 15 minutes of running wide open it slowley looses power and then dies and is hard to start back up. i need some suggestions please

[AMD Rules]

Did you open the vent on the fuel tank? Classic symptom you described.

If you pump the fuel bulb when its slowing down, does it help? This is a sign of a weak fuel pump.

Any filters or screens on the fuel system between the tank and the motor? Sounds like its starving for fuel.

Does the fuel bulb go firm when you prime it? Hard starting could be a sign of a malfunctioning check valve in the primer bulb. Fuel drains back to the tank, and becomes hard to start. A warm motor should start right up easily.

Could be overheating.... telltale water stream look okay? Impeller changed recently? Motor appear to be running hot?

[nshirley1022]

it has a metal gas tank dont know if it has a openable vent. it has a inline fuel filter could that be a problem. i dont think it is getting hot.

[nshirley1022]

the guy who owned it before me put on a brand new prop used to be plastic

[AMD Rules]

All fuel tanks must have a vent. If its not vented, the vacuum built up in the tank as it runs will eventually cause the motor to slow down and stop.

Portable tanks have a vent you can open & close. Permanent tanks are always vented.

Check it out... if you're lucky thats all it is.

[nshirley1022]

i checked the tank the vent was closed could this possabaly be all that was wrong with it.
thanks

[AMD Rules]

Most likely.