Fuel Pump Bad?

[meat]

I have a boat that sat for about 4 years without use. It has a Volvo Penta AQ231B (305 GM). I have it running but it still wants to idle rough and its rpm's fluctuate but it seems to improve at higher rpm. <br /><br />Before I ran it I pumped out all the old gas and performed all its regular maintenance along with prepping it for running after years of no use. Along with a new starter and battery.<br /><br />I went ahead and rebuilt the carburetor and the compression checks out good.<br /><br />However, when I changed the oil after sitting so many years it definitely had the scent of fuel in it and my first thought was a float in the carb was stuck. But now I am thinking the diaphragm in the fuel pump may be bad. Especially considering the pump is 15 years old and sat for years. Could this be causing my problems? It is a mechanical pump.<br /><br />Also, the ballast resistor seems to get really hot. Have not had much experience with them but how hot should they get?<br /><br />Thanks.

 

[Don S]

Re: Fuel Pump Bad?

Yes the fuel pump will cause fuel in the oil. Be sure to replace it with a marine fuel pump, not automotive. <br />Yes also to the ballest resistors, they do get hot.

 

[meat]

Re: Fuel Pump Bad?

Thanks for the quick response Don.<br /><br />I will look up the part number for it with Volvo Penta. However, is a same mechanical replacement recommended or an upgrade to an electric pump? Any advice or suggests on that? I know the Volvo Penta mechanical ones sell for around $80.<br /><br />I am also thinking the fluctuating rpm issue has to do with the fuel pump as well.<br /><br />Thanks.

 

[Olds Eddie]

Re: Fuel Pump Bad?

A mechanical pump is safer IMHO as it only works when the motor is running. An electrical pump will run even if the engine quits and if you have a leak in the pressure side of the fuel system it will fill your bilge with gas. Not a good thing. <br />Did you soak your carb in a bucket of carb cleaner when you re-built it? The surge could be caused by varnish build up in internal passages. This is what happens to carbs when stored for a long time with treating the fuel with stabilizer.

 

[Don S]

Re: Fuel Pump Bad?

A mechanical pump is safer IMHO as it only works when the motor is running. An electrical pump will run even if the engine quits and if you have a leak in the pressure side of the fuel system it will fill your bilge with gas. Not a good thing.

Not Exactly True.<br />All it takes is an oil pressure switch on the input power. When there is oil pressure, there is power to the fuel pump. If the oil pressure goes below 5 lbs, the switch opens and the fuel pump stops running.<br />That is how Mercruiser has been doing it for years.<br /><br />In this diagram, 5 is the oil pressure switch and 6 is the fuel pump.<br /><br />