onan fuel pump problems

[monk47438]

Hey guys, 

first post here.  I have a L600 with the onan b48m engine. It  has the diaphragm fuel pump mounted to the carb. It has quit pumping fuel.  I have rebuilt the diaphragm with a kit several times and cant get it to work? any ideas?  runs great if you pour gas down the carb throat.   Thanks

[David Banker]

I have one of those Onans in a railcar.  I have gone to using a separate electric fuel pump.

On Monday, February 27, 2023 at 12:50:24 PM MST, monk47438 <mi...@bigtimberworks.com> wrote:

Hey guys, 

first post here.  I have a L600 with the onan b48m engine. It  has the diaphragm fuel pump mounted to the carb. It has quit pumping fuel.  I have rebuilt the diaphragm with a kit several times and cant get it to work? any ideas?  runs great if you pour gas down the carb throat.   Thanks

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[mfmcallister]

Mike, 

If you want to put the time in, start by eliminating issues. Does the diaphragm actually work?  Put a new short hose on the carb and put it in a gas can filled with new gas. Position the can on a chair so the hose is just below your carb to see if it will suck the gas up. If that works, put a longer new hose on it and put the can on the floor. If it still works, then your pump works with enough vacuum to pull the gas from your tank. I'd then check for a clogged gas hose, clogged fuel filter, a leak in the hose/connections causing the pump to suck air. The gas in the tank could be bad. Has water gotten the tank?  Has the gas cap been replaced? The older style caps these came with had a vent hole in the top. My Dad's L600 is 46 years old. It has never beed garaged, sat for 25 years. The gas tank bottom was rusted out had he had to rebuild it, replaced the bottom, the pipes and added a vent hose like the newer models have. It is possible that the pipe in your gas tank is clogged or has rusted hole above the level of the gas allowing the pump to suck gas vapors. If the only issue is that the vacuum pump does not work, do as Dave says and install and electric fuel pump. My father also had issues with 2 Onan 16hp carbs so he installed a cheap electric fuel pump instead of locating and buying a diaphragm kit. It worked but I believe the pressure (7psi) was too much for that small engine. It would run ok for a while then almost die then be ok again. If you get a electric fuel pump, get a fuel regulator. A previous post mentions that 2-3 psi is the most pressure a diaphragm fuel pump would put out. Another post mentions an adjustable 1-5 psi regulator is available to address the issue. - Mark

[mfmcallister]

Mike, I found a YouTube video showing how to install a Briggs vacuum pump instead of an electric pump on your Onan engine. https://www.youtube.com/watch?v=aIplbF3CEcg

This may be cheaper and quicker fix than buying an electric pump and regulator if needed. - Mark