Question about Watts Onan Portable Generator - 4000 , Model# 5500

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Onan 5500. Has spark. Has fuel. Has oil. Will start and run for a few moments after spraying starting fluid into air intake. It appears that as long as the correct mixture of starting fluid is administered it would continue to run. The problem with that process is that as you spray the fluid into the intake the mixture is to rich. As the engine continues to turn, start switch engaged, it will finely become lean enough to run for a few seconds. If you could supply the correct mixture ratio for more than a few seconds it appears it would continue to run. The Onan 5500 was running and suddenly quit. It had been started/run a few times over the week long trip when it simply stopped running and would not restart. I have read several posts and it could be the low oil sensor, the control board, or the varnish build up in the carburetor. What do you suggest beyond that if anything.

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  • w0glt Sep 04, 2010

    All great advise. Where is the control board located and how do you get to it? Do you know a web site URL address where the service manual can be downloaded for this Onan series BGM / H?



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If it starts when you add fa fuel source to the carb throat it is not the oil level sensor. The oil level sensor and generator fault circuits all shut off the spark. You have a fuel blockage most likely in the carb float bowl caused by debris / corrosion that has made its way into the fuel jet orifice located inside the hole that the fuel bowl nut threads into into. Get some carb cleaner and shoot into the hole that the float bowl nut threads into. Make sure you dump the fuel float bowl contents. With the bowl removed use a spray can lid or something similar to check fuel flow. Fuel selector on float down you should have fuel flow. Genyly lifting the float to level the fuel flow should stop.
If you do not have any fuel flow then there is a problem with the fuel supply. Remove the fuel supply hose at the carb. Feul should flow freely. Good flow from hose = float needle problem.
No flow from hose = check fuel filter and fuel tank outlet / fuel selector for debris.

If you have checked all of the above then jumper pins 5 to 9 on the main board. You should hear the fuel pump running. If you don't hear it running then the fuel pump has probably failed.

Reconnect and re-install everything and fuel leak test before starting.

Thanks for choosing FixYa.


Posted on Sep 03, 2010

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  • Kelly
    Kelly Sep 04, 2010

    This is about the best I can do for a free manual without refering you to a pay to download site:

    Note the pin-out checks in the manual. Don't be afraid to open the power panel acess engine off.


  • Kelly
    Kelly Sep 04, 2010

    The service manual for your generator is 965-0528 I do not have it in electronic format and was not abote to locate a freebie either. I think the manual new cost me like $18.00. It has paid for itself many times over. Every Onan 4000 owner should have one. The owners manual is useless for any thing other than routine service.


  • Kelly
    Kelly Sep 04, 2010

    Just a note here. Your generator must have oil pressure and AC output available to run. I still think you have a fuel supply problem either from the fuel pump not running or... debris some where in the fuel system including the float bowl and orifice.




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