Home » Public Forums » GMCnet » Relocate Onan Fuel Pump?
| Relocate Onan Fuel Pump? [message #323291] |
Mon, 04 September 2017 11:47  |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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The Onan on my Royale takes 10-12 seconds to fire off after it's been off for a few days. After it's started once, restarts within a day or so are immediate.
Choke solenoid is working, existing fuel pump is a Facet ice cube 40104 mounted at the factory location that supposedly has a check valve. I figure either the check valve leaks a little, or there's a leak in the line (I don't see evidence of a leak).
Would relocating the pump near and below the fuel tank tap improve cranking time - thinking that the pump likes pushing rather than sucking?
Also, since the original pump had a filter, I figure I'd add one just downstream of the pump.
Thoughts?
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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| Re: [GMCnet] Relocate Onan Fuel Pump? [message #323298 is a reply to message #323291] |
Mon, 04 September 2017 12:15  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Go to our web sight under ONAN and see the prime switch.
It was developed by our late Duane Simmons, and lot of us love it as we
press the button fo several seconds first then hit the starter.
These are things you learn at tech seminars at club and regional get
togethers.
Also look us up on our web site to see what options are available.
You can get them from other suppliers as well.
On Mon, Sep 4, 2017 at 9:47 AM, Bill Van Vlack
wrote:
> The Onan on my Royale takes 10-12 seconds to fire off after it's been off
> for a few days. After it's started once, restarts within a day or so are
> immediate.
>
> Choke solenoid is working, existing fuel pump is a Facet ice cube 40104
> mounted at the factory location that supposedly has a check valve. I figure
> either the check valve leaks a little, or there's a leak in the line (I
> don't see evidence of a leak).
>
> Would relocating the pump near and below the fuel tank tap improve
> cranking time - thinking that the pump likes pushing rather than sucking?
>
> Also, since the original pump had a filter, I figure I'd add one just
> downstream of the pump.
>
> Thoughts?
> --
> Bill Van Vlack
> '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath,
> Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o
> mid
> November 2015; Since arrival: New HVAC blower, heat flap cable, headlight
> switch.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Relocate Onan Fuel Pump? [message #323301 is a reply to message #323291] |
Mon, 04 September 2017 12:24 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I had the same problem last week on the generator from hell. We installed a new one of those pumps and every morning had the problem. I cleaned up the old pump and installed a new gasket and filter in the old pump. After re-installing the old one we never had a another problem. In my opinion, I would fix the old pump or buy another one like it.
Jim K at Applied GMC has the correct replacement pump.
You can also add a prime button circuit and prime the carb before starting.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Relocate Onan Fuel Pump? [message #323302 is a reply to message #323291] |
Mon, 04 September 2017 12:31 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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Thanks, Jim.
I'm aware and familiar with the prime button solution but am reluctant to modify the Royale monitoring and control panel by drilling a hole for a button on or near it.
I tried searching for a discussion on this issue, but didn't find one, hence the question.
I'm guessing from the development and sale of the prime button that perhaps a solution to the cause of the Onan slow starting is not known or difficult to solve?
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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| Re: Relocate Onan Fuel Pump? [message #323303 is a reply to message #323302] |
Mon, 04 September 2017 12:39 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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Ken,
I wish I had the original pump; it seems fairly foolproof and easy to repair. Do you (or Jim) know if the replacement pump is repairable (filter, clean ball check, gasket) or is it a sealed unit?
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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| Re: [GMCnet] Relocate Onan Fuel Pump? [message #323311 is a reply to message #323302] |
Mon, 04 September 2017 14:11 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Sep 4, 2017, at 1:31 PM, Bill Van Vlack wrote:
> I'm guessing from the development and sale of the prime button that perhaps a solution to the cause of the Onan slow starting is not known or difficult to solve?
As I see it there are two problems that must be addressed:
1. Evaporation of the fuel inventory in the carb bowl after engine shutdown due to heat soak.
2. Drain back of the fuel from the fuel pump to the main tanks via gravity after shutdown.
Fixing #2 sort of provides a solution to #1. The original Onan design had an electric fuel solenoid valve between the tank and the Bendix/Facet pump; when the Onan was turned off this valve would close and hold an inventory of fuel above the valve in the pump chamber - and upon startup this fuel only had to travel a very short distance to the carb in order to get the engine started. Once the engine started the fuel pump would have time to bring fuel from the relatively far-away main vehicle tanks while the unit was running on the fuel in the bowl.
Some have eliminated the solenoid valve for whatever reason - this means they will be starting the Onan with an empty fuel line all the way to the vehicle tanks and without a primer button they’ll have to crank and crank and crank in order to give the fuel pump time to re-prime the lines.
Other people took off the cylindrical Bendix pump that had the large pump chamber and replaced it with a cube pump which has no pump chamber. I realize these are supposed to check internally - the problem is that they don’t have enough inventory above the check valve to fill the carb at start time. I’d say units with the cube pump should have a primer button installed for the same reason stated above.
Designers of the Onan knew about subtle things like the problems described above and they chose specific components to address them. Those who second-guess the designers will have to discover and solve those subtle problems all over again and will inevitably be frustrated in the process.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Relocate Onan Fuel Pump? [message #323316 is a reply to message #323291] |
Mon, 04 September 2017 14:40 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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Jim,
Thanks for the analysis... So the chamber provides a reservoir until the pump can draw from the tank and catch up, it seems. It sounds like the check valve (in either case) isn't sufficient to prevent the fuel between the pump and the tank from draining back in spite of the 'straw' effect.
I can see why Onan would want to have the generator self-contained and not require an external fuel pump, but isn't relocating the cube pump to a flooded location an option as well at this point? It seems that if the chamber/check in the factory pump can hold fuel 'up', then the cube pump check could as well.
But if it's known that the original pump/chamber/check works, that's the best answer. Now to find one (I'm assuming the modern versions aren't as good).
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
[Updated on: Mon, 04 September 2017 14:42] Report message to a moderator |
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| Re: Relocate Onan Fuel Pump? [message #323331 is a reply to message #323291] |
Mon, 04 September 2017 17:44 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I have no prime button. After months of sitting I count about 6 rotations cranking and it's running. When run recently it starts as soon as you touch the start button.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Relocate Onan Fuel Pump? [message #323336 is a reply to message #323331] |
Mon, 04 September 2017 17:51 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Sep 4, 2017, at 6:44 PM, John R.Lebetski wrote:
> I have no prime button. After months of sitting I count about 6 rotations cranking and it's running. When run recently it starts as soon as you touch the start button.
Hi John,
What sort of pump do you have? And do you still have the fuel solenoid valve?
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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