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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 5.5BGM Generator


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  #1  
Old 02-23-2018, 09:31:44 AM
66vette 66vette is offline
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Default Onan 5.5BGM Generator

I am looking for information in regard to rewiring the fuel pump to prime the pump prior to starting the Generator to eliminate having to crank the engine for some time to get fuel to the carburetor. My thoughts are to add a momentary push button switch to provide power to the fuel pump. Has anyone done this without causing other electrical problems. I did this to my previous Kohler Generator with no issues, but the Kohler was an older model, did not have all of the electronics of the more modern Onan.
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Old 02-23-2018, 09:57:07 AM
Kevin K Kevin K is offline
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Default Re: 5.5BGM Onan Generator

I have done that to every one of my Onans. I use a spring loaded SPDT (Single Pole Double Throw) switch to switch the fuel pump power from the control board to battery voltage. You can get a center off switch if you desire to allow the engine to run the carburetor out of gasoline.

If you want any more specific information you will need to provide the full model and serial numbers.
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Old 02-24-2018, 12:10:50 PM
66vette 66vette is offline
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Default Re: 5.5BGM Onan Generator

I was thinking of using a spring loaded normally off SPST switch from a 12 volt line. Didn't know if I had to place a diode in the existing 12 volt line to eliminate feed back to any electronic component. Why did you use a SPDT switch?
My specs are as follows:
Model 5.5BGMFA26105H
Serial I990985684
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Old 02-24-2018, 12:19:59 PM
DMeed DMeed is offline
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Default Re: 5.5BGM Onan Generator

I think he used a spdt switch with a momentary position. Or maybe he meant a sptt (single pole, triple throw)

It would normally be in the on position where it feeds power to the fuel pump from the normal circuit.

It could be set to the middle or off to turn off the fuel pump at the end of a run and allow the gasoline to be emptied out of the carburetor bowl before shutting down

It can be held to the (momentary) on position the other way to do what you are looking for and running the fuel pump without the engine running to prime the gasoline system.

With a switch like this you don't have to worry about backfeeding anything because as soon as you switch it off the normal run position, it disconnects from that circuit and isolates the pump.

What you are talking about (a momentary switch between the battery and the fuel pump) doesn't disconnect the line going to the control board, so yes you would have to figure out if it would backfeed anything on the control board.
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Old 02-24-2018, 02:53:34 PM
66vette 66vette is offline
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Default Re: 5.5BGM Onan Generator

You are correct with using the switch he was proposing you would have the option to not have any voltage to the pump to run the carburetor dry also would eliminate the feedback issue. I believe that would be the way to go. Thanks for all of the replies.

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Originally Posted by 66vette View Post
You are correct with using the switch he was proposing you would have the option to not have any voltage to the pump to run the carburetor dry also would eliminate the feedback issue. I believe that would be the way to go. Thanks for all of the replies.
I can also see the need for a double pole switch since you have to have the original 12 volt wire on one side of the middle pole along with an all time hot wire on the other center pole. One side of the switch would be for the original wiring and when you switch to the momentary side the other side of the switch would be for that circuit, the center position would be off for both circuits.

A single pole double throw would also work by fastening the wire going to the pump on the center post and the hot 12 volt on one end and the original 12 volt at the other end post.
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Old 02-24-2018, 03:14:13 PM
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Default Re: 5.5BGM Onan Generator

On my CCK, I used a momentary push button switch. You CAN put a 5 amp diode between the factory fuel pump wiring and the fuel pump. Remember this too, cranking the set also primes the oiling system and lubricates the journals, rods and cam BEFORE it starts.
When I worked at UPS, I had a 20 year old package car with a well worn Ford 300 6 cyl engine. The truck had hand choke. When you cranked it immediately with the choke pulled, it started and rattled to beat hell. I would instead let it crank for about 5-10 seconds THEN pull the choke and the old girl came to life without a single rattle. That old "6" was the fastest old package car and the engine lasted me until they retired the car and CRUSHED it.
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Old 02-24-2018, 07:38:51 PM
Pete Spaco Pete Spaco is offline
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Default Re: 5.5BGM Onan Generator

I prefer the SPDT center off switch. That way I don't have to "tend" the fuel pump until it primes.
I made a little bracket to hold the switch with wide enough flat spots so I could label one side "Prime" and the other side "Run". I figured that, even with my poor memory, I'd know that the center was "Off".
It doesn't hurt to leave the switch in the "prime" position while the engine is running, as long as you turn it to Off or to Run when you are done. But the reason that I use "center off" is that I use woodgas for fuel once the engine is warmed up, so I need a position where the fuel pump is totally off.

Pete Stanaitis
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Old 03-06-2018, 02:18:31 PM
66vette 66vette is offline
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Default Re: 5.5BGM Onan Generator

With the weather getting better in Ohio, I looked at wiring the Generator today, based of what I am seeing it looks like I have to pull the Generator out of the Motorhome to get to the fuel pump. I was hoping to be able to get to the wiring from the front of the Generator. I am looking for ideas and assistance for those that have done this without pulling the Generator.
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