Home » Public Forums » GMCnet » [GMCnet] Onan electric gas shut off valve just before the fuel pump.
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310932 is a reply to message #310930] |
Sat, 26 November 2016 10:16 |
Ken Burton
Messages: 10030 Registered: January 2004 Location: Hebron, Indiana
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A lot of people have removed them. I do see a reason why you might want to keep it. Especially on a Royale.
On a Royale the gas feed to the Onan is "Teed" into the same main tank feed line that feeds the 403/455 engine. If the float in the Onan carb is down allowing the needle and seat valve to remain open, it is possible that the main engine fuel pump could draw fuel and eventually air back through the Onan fuel line.
I'm not positive that the Onan inline fuel pump would allow this to happen but it is a something to think about.
I have never tried to move fuel in a reverse direction through one of those pumps. We do move fuel in a forward direction through one of those pumps all the time on low wing airplanes. On a low wing airplane, fuel is pumped by a mechanical pump on the engine and the electric pump is normally turned off. The electric is only turned on in the case of a mechanical pump failure.
On a GM built coach (not transmode) the fuel to the Onan is pulled from a different port on the main tank so this issue should not exist with the valve removed..
It is something to think about.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310936 is a reply to message #310931] |
Sat, 26 November 2016 12:25 |
Jim Miller
Messages: 501 Registered: March 2008
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On Nov 26, 2016, at 10:59 AM, A. wrote:
> The valve does not have a purpose on the GMC. Onan made them standard in case the generator is installed with the gas tank above the carburetor. Remove it and eliminate a potential point of failure.
With all due respect, the valve DOES have a purpose. It prevents the fuel inventory in the pump’s inlet chamber from being drained back to the tank via siphon action - thus permitting the unit to achieve a successful start with less cranking.
Remember that the GMC as it came from the factory was not provided with a primer button - so with an empty pump chamber you would be cranking the engine with no chance of it starting while the pump was bringing a new inventory of fuel up from the tank. The design was such that it would be easy for a non-mechanically-oriented GMC owner to get it to start without fiddling around.
I installed the primer button on my coaches AND I kept the solenoid valve. Even if the valve were to go bad it would only take about 2 minutes to remove it and stick the hose right on to the pump inlet.
One could always try to find a check valve to replace the solenoid…
—Jim
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310937 is a reply to message #310936] |
Sat, 26 November 2016 12:37 |
Ken Burton
Messages: 10030 Registered: January 2004 Location: Hebron, Indiana
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Jim Miller wrote on Sat, 26 November 2016 12:25On Nov 26, 2016, at 10:59 AM, A. wrote:
> The valve does not have a purpose on the GMC. Onan made them standard in case the generator is installed with the gas tank above the carburetor. Remove it and eliminate a potential point of failure.
With all due respect, the valve DOES have a purpose. It prevents the fuel inventory in the pump's inlet chamber from being drained back to the tank via siphon action - thus permitting the unit to achieve a successful start with less cranking.
Remember that the GMC as it came from the factory was not provided with a primer button - so with an empty pump chamber you would be cranking the engine with no chance of it starting while the pump was bringing a new inventory of fuel up from the tank. The design was such that it would be easy for a non-mechanically-oriented GMC owner to get it to start without fiddling around.
I installed the primer button on my coaches AND I kept the solenoid valve. Even if the valve were to go bad it would only take about 2 minutes to remove it and stick the hose right on to the pump inlet.
One could always try to find a check valve to replace the solenoid...
--Jim
1977 Eleganza
1977 Royale
Hamilton, OH
Jim,
Will the gas travel backwards through the pump? I think the answer is yes because on several occasions when I have had the gas line disconnected at the carb all of the gas flowed out of te line and back to the tank. Then I had to prime and prime to get it pumping again.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310941 is a reply to message #310936] |
Sat, 26 November 2016 15:36 |
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USAussie
Messages: 15912 Registered: July 2007 Location: Sydney, Australia
Karma: 6
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Jim,
I don't disagree with you, however, I direct your attention to Parts Book 78Z / Section 28 - Furnishings / Page 28-51 / Figure
28.044E - Pump - Fuel, Onan Generator / Key 8 - Spring - cup and valve
Isn't this part a check valve that only allows the fuel to flow in one direction when the piston shuttles back and forth? If it
didn't I don't understand how the pump would pump.
The reason I don't disagree with you is because the check valve may allow fuel to slowly seep past it.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Jim Miller
Sent: Sunday, November 27, 2016 5:26 AM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump.
With all due respect, the valve DOES have a purpose. It prevents the fuel inventory in the pump's inlet chamber from being drained
back to the tank via siphon action - thus permitting the unit to achieve a successful start with less cranking.
Remember that the GMC as it came from the factory was not provided with a primer button - so with an empty pump chamber you would be
cranking the engine with no chance of it starting while the pump was bringing a new inventory of fuel up from the tank. The design
was such that it would be easy for a non-mechanically-oriented GMC owner to get it to start without fiddling around.
I installed the primer button on my coaches AND I kept the solenoid valve. Even if the valve were to go bad it would only take about
2 minutes to remove it and stick the hose right on to the pump inlet.
One could always try to find a check valve to replace the solenoid.
Jim
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310956 is a reply to message #310941] |
Sat, 26 November 2016 20:52 |
Jim Miller
Messages: 501 Registered: March 2008
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On Nov 26, 2016, at 4:36 PM, Rob Mueller wrote:
> I don't disagree with you, however, I direct your attention to Parts Book 78Z / Section 28 - Furnishings / Page 28-51 / Figure 28.044E - Pump - Fuel, Onan Generator / Key 8 - Spring - cup and valve
>
> Isn't this part a check valve that only allows the fuel to flow in one direction when the piston shuttles back and forth? If it didn't I don't understand how the pump would pump.
Hi Rob,
Yes, the pump does have a check valve that is fundamental to its operation and there may or may not be some fuel captive about it and in the hose going up to the carb. Considering that the compartment temperature can go north of 210F after shutdown (it is much less during operation and I have experimentally measured it under both operational conditions) then some or all of that fuel might have boiled off after the last run.
The inlet fitting in the side of the pump body leads into a plenum area where the mesh filter basket is located and this location can hold an additional bit of fuel not to mention the fuel that is captive between the solenoid valve and the pump inlet.
In addition to the faster-starting issue that I raised, KenB also brings up a point why it would be beneficial on certain model coaches to have the line closed hard by the valve.
I’ve worked on vehicles for 40 years and I have rarely if ever seen a superfluous component (especially a relatively expensive one) on any of them. If GM or Onan put the valve there then they did so for a reason which may or may not be obvious to observers decades later.
—Jim
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310957 is a reply to message #310956] |
Sat, 26 November 2016 22:00 |
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USAussie
Messages: 15912 Registered: July 2007 Location: Sydney, Australia
Karma: 6
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Jim,
You're right!
I had not considered the location of the pump check valve in the fuel flow stream. With the solenoid removed there is nothing to
stop the flow of fuel from the pump back into the gas tank.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Jim Miller
Sent: Sunday, November 27, 2016 1:53 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump.
Hi Rob,
Yes, the pump does have a check valve that is fundamental to its operation and there may or may not be some fuel captive about it
and in the hose going up to the carb. Considering that the compartment temperature can go north of 210F after shutdown (it is much
less during operation and I have experimentally measured it under both operational conditions) then some or all of that fuel might
have boiled off after the last run.
The inlet fitting in the side of the pump body leads into a plenum area where the mesh filter basket is located and this location
can hold an additional bit of fuel not to mention the fuel that is captive between the solenoid valve and the pump inlet.
In addition to the faster-starting issue that I raised, KenB also brings up a point why it would be beneficial on certain model
coaches to have the line closed hard by the valve.
I've worked on vehicles for 40 years and I have rarely if ever seen a superfluous component (especially a relatively expensive one)
on any of them. If GM or Onan put the valve there then they did so for a reason which may or may not be obvious to observers decades
later.
-Jim
1977 Eleganza
1977 Royale
Hamilton, OH
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #310973 is a reply to message #310936] |
Sun, 27 November 2016 07:26 |
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Matt Colie
Messages: 8547 Registered: March 2007 Location: S.E. Michigan
Karma: 7
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Jim Miller wrote on Sat, 26 November 2016 13:25With all due respect, the valve DOES have a purpose. It prevents the fuel inventory in the pump's inlet chamber from being drained back to the tank via siphon action - thus permitting the unit to achieve a successful start with less cranking.
Remember that the GMC as it came from the factory was not provided with a primer button - so with an empty pump chamber you would be cranking the engine with no chance of it starting while the pump was bringing a new inventory of fuel up from the tank. The design was such that it would be easy for a non-mechanically-oriented GMC owner to get it to start without fiddling around.
I installed the primer button on my coaches AND I kept the solenoid valve. Even if the valve were to go bad it would only take about 2 minutes to remove it and stick the hose right on to the pump inlet.
One could always try to find a check valve to replace the solenoid...
--Jim
1977 Eleganza
1977 Royale
Hamilton, OH
To those thinking that the check valves in the Bendix clicker pump should do the job, remember that when the pump is dead headed, it keeps clicking.....
That means it has to have internal leakage. Indeed, in my experience, they all do.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312068 is a reply to message #310930] |
Thu, 12 January 2017 17:31 |
kwharland
Messages: 246 Registered: November 2005 Location: Central Florida
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Interesting discussion. I was just working on mine and was thinking the valve wasn't opening because the pump wouldn't prime the carb so I pulled the valve and found it was in fact failed....open! Fuel just flows straight through it when held vertically and disconnected from power. Who knows how long it's been like that.
But as to the point that the carb fuel will be drawn down without the solenoid valve, that's not possible as the fuel inlet on the carb is above the fuel level in the bowl. It certainly can evacuate the pump and filter if you use one but none of those will delay starting if the carb bowl is full. I also doubt that air flowing back through the system can starve the motor driven fuel pump but that's only a hunch. Easy enough to put a vacuum gauge on the line and see which brings me to the point of my post...how much suction is the Onan pump supposed to produce?
Mine has very little and I didn't have my gauges handy to check but I really had to pay close attention to see that there's any at all. It hasn't been long since I disassembled and cleaned it so I doubt it's fouled but the check valves could be leaky from age.
As an aside, you know how you start to tackle one specific problem and pretty soon you're up to your neck in issues? My goal today was to test the low oil pressure switch since the Onan would start but shut off as soon as you released the start switch. As I sat on the ground beside the genset, I figured I might as well pull the side cover off to expose the pressure switch while I was taking the cover off the control board. Well don't you know it...one of the bolts holding the cover snapped off flush in the head with the slightest pressure.
So I stopped there and got my drill, left-hand drill bits, tap, sharp punch, hammer and propane torch. A little later the remains of the bolt were extracted and threads cleaned up. I reseated the connector on the pressure switch just to make sure and then tried to start the generator and no dice! It started fine a few days ago. Grabbed a 12 V source and attempted to prime the carb and the pump ran continuously building no back pressure unlike a few days ago. That launched me on the troubleshooting of the solenoid valve. I don't imagine they pull much vacuum but it appeared mine couldn't pull any fuel from a nearly full tank.
1978 Eleganza II
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312069 is a reply to message #312068] |
Thu, 12 January 2017 18:50 |
Jim Miller
Messages: 501 Registered: March 2008
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On Jan 12, 2017, at 6:31 PM, Ken Harland wrote:
> But as to the point that the carb fuel will be drawn down without the solenoid valve, that's not possible as the fuel inlet on the carb is above the
> fuel level in the bowl. It certainly can evacuate the pump and filter if you use one but none of those will delay starting if the carb bowl is full.
Hi Ken,
You are correct in that in the absence of the solenoid valve the siphon induced by fuel dropping back into the tank can drain the pump but not the carb bowl.
Keep in mind that the temperature in the Onan compartment stays very near ambient while the machine is running due to massive cooling airflow - however the temperature rises rapidly and considerably once the machine is shut down; the sustained heat soak after shutdown can vaporize some (or perhaps all) of the fuel inventory that was left in the bowl. Crappy ethanol-laced gas exacerbates this effect (ask the people whose main engine suffers from vapor lock).
I was curious about the temperatures in the Onan enclosure so I instrumented my compartment with thermocouples to see exactly what was going on. I found that on an 80F day the compartment reached almost 220F directly above the exhaust manifold immediately after the unit was shut off. The carb, being on top of the engine, will be subject to the same temperature extremes and therefore fuel evaporation out of the bowl could be an issue for subsequent starts.
My temperature measurement results are here: http://www.jcmco.com/gallery/album29
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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1977 Eleganza II
1977 Royale
Hamilton, OH
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312070 is a reply to message #312069] |
Thu, 12 January 2017 18:59 |
Emery Stora
Messages: 959 Registered: January 2011
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Thanks, Jim. Good information.
I would like to point out that the Onan was running with the drawer and cover door closed.
Some people think that their Onan will run cooler with the door propped open and the Onan extended on its slides.
I have often seen them running this way at campgrounds.
However, as your data shows, the massive cooling airflow is achieved with the Onan tucked into its enclosure with the compartment door closed.
Emery Stora
77 Kingsley
Frederick, CO
> On Jan 12, 2017, at 5:50 PM, Jim Miller wrote:
>
> On Jan 12, 2017, at 6:31 PM, Ken Harland wrote:
>
>> But as to the point that the carb fuel will be drawn down without the solenoid valve, that's not possible as the fuel inlet on the carb is above the
>> fuel level in the bowl. It certainly can evacuate the pump and filter if you use one but none of those will delay starting if the carb bowl is full.
>
>
> Hi Ken,
>
> You are correct in that in the absence of the solenoid valve the siphon induced by fuel dropping back into the tank can drain the pump but not the carb bowl.
>
> Keep in mind that the temperature in the Onan compartment stays very near ambient while the machine is running due to massive cooling airflow - however the temperature rises rapidly and considerably once the machine is shut down; the sustained heat soak after shutdown can vaporize some (or perhaps all) of the fuel inventory that was left in the bowl. Crappy ethanol-laced gas exacerbates this effect (ask the people whose main engine suffers from vapor lock).
>
> I was curious about the temperatures in the Onan enclosure so I instrumented my compartment with thermocouples to see exactly what was going on. I found that on an 80F day the compartment reached almost 220F directly above the exhaust manifold immediately after the unit was shut off. The carb, being on top of the engine, will be subject to the same temperature extremes and therefore fuel evaporation out of the bowl could be an issue for subsequent starts.
>
> My temperature measurement results are here: http://www.jcmco.com/gallery/album29
>
> —Jim
>
> Jim Miller
> 1977 Eleganza
> 1977 Royale
> Hamilton, OH
>
>
>
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312071 is a reply to message #312070] |
Thu, 12 January 2017 19:17 |
Jim Miller
Messages: 501 Registered: March 2008
Karma: 10
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Hi Emery,
I’m subscribed to the email list and Ken’s message that I replied to is the first I’ve seen with this particular subject; therefore I do not know the whole back story.
Maybe some messages are not making it from the forum to the email list?
I would not run my Onan extended out on its slides unless I had a good reason to do so however I see no harm (and perhaps some potential benefit) to running the unit with the door open if circumstances permitted me to do so. The engine will receive the same cooling airflow while operating no matter whether the door is open or closed - but after shutdown the hot air would convectively flow right out of the compartment through the open door thus cooling things off more rapidly and preventing loss of fuel inventory in the bowl.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
> On Jan 12, 2017, at 7:59 PM, Emery Stora wrote:
>
> Thanks, Jim. Good information.
>
> I would like to point out that the Onan was running with the drawer and cover door closed.
>
> Some people think that their Onan will run cooler with the door propped open and the Onan extended on its slides.
> I have often seen them running this way at campgrounds.
>
> However, as your data shows, the massive cooling airflow is achieved with the Onan tucked into its enclosure with the compartment door closed.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312073 is a reply to message #312072] |
Thu, 12 January 2017 20:07 |
Jim Miller
Messages: 501 Registered: March 2008
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On Jan 12, 2017, at 8:42 PM, Ken Harland wrote:
> Jim, this thread started in Nov 2016 and the last post before mine was still that month so maybe that's why you don't recognize it.
Yes Ken, that must be it. I’ve archived GMCnet 2016 and therefore didn’t see the rest of the thread. Thank you.
Strange, though….your sentence I quoted above was all that came through the email reflector to my mailbox. Yet, when I look at the forum there’s an additional sentence - “Still hoping someone has suction specs for the Onan pump”.
I do not know that *suction* specs were published for the pump nor have I ever tried to measure it as it seems kind of a meaningless indicator of performance in this particular application. I can tell you, however, that I measured the pump's *discharge* pressure fluctuating at 1-2 psi on an operational Onan that was fully loaded at 6kW. HTH.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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1977 Eleganza II
1977 Royale
Hamilton, OH
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312074 is a reply to message #312073] |
Thu, 12 January 2017 20:24 |
kwharland
Messages: 246 Registered: November 2005 Location: Central Florida
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Hi Jim,
Not sure I understand your statement "it seems kind of a meaningless indicator of performance in this particular application". The pump has to be able to draw fuel from the tanks and to do so must create some level of suction. Mine seems weak but without some guidance I can't assess whether it's adequate or I have a different problem upstream.
1978 Eleganza II
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Re: [GMCnet] Onan electric gas shut off valve just before the fuel pump. [message #312077 is a reply to message #312074] |
Thu, 12 January 2017 20:36 |
Jim Miller
Messages: 501 Registered: March 2008
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On Jan 12, 2017, at 9:24 PM, Ken Harland wrote:
> Not sure I understand your statement "it seems kind of a meaningless indicator of performance in this particular application". The pump has to be
> able to draw fuel from the tanks and to do so must create some level of suction. Mine seems weak but without some guidance I can't assess whether
> it's adequate or I have a different problem upstream.
Why not just measure the discharge pressure? If you google: facet bendix fuel pump ….then you’ll find that their output pressure, operating voltage and pipe fitting size are specified...not their suction ability.
If we were talking about a vacuum pump or a well water pump then suction specs might be interesting but in the case of the Onan we’re talking about a foot or less of lift from the main fuel tank to the pump. I’m more interested in the pump’s ability to push fuel into the bowl without so much pressure to overrun the needle/seat. Just my $0.02.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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1977 Eleganza II
1977 Royale
Hamilton, OH
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