Home » Public Forums » GMCnet » Use a vented Fuel Pump?
| Use a vented Fuel Pump? [message #337933] |
Tue, 16 October 2018 18:55  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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There are two fuel pumps for 455.
One has a metered vent line, these are not the part for our coaches.
The other has no vent provision.
Because of fate's intervention, I now have a coach with the wrong pump. (I am thinking this is temporary.)
To combat vapor lock, has anyone ever taken that vent fitting and piped over to the fill vent line(s) that are in the left rear of the engine space?
There were a plethora of such things done in the mid-70s when engine space temperatures went up. They were known to have varying degrees of success.
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: Use a vented Fuel Pump? [message #337934 is a reply to message #337933] |
Tue, 16 October 2018 19:08  |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Using the vented (fuel return) type pumps was one of the things we used to use to help avoid vapor lock in the 'dark ages'. Living in Las Vegas it was always a problem during warmer months even with real fuel. It did seem to help in most cases but we didn't have to deal with the quality of fuel we are forced to use today. Using an electric pump together with the return would probably be a good combination.
Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: Use a vented Fuel Pump? [message #337935 is a reply to message #337933] |
Tue, 16 October 2018 19:16 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Dave Lenzi once recommended those pumps to help combat vapor lock, but you probably need to tap in a fitting to the filler tube for the return line rather than the vent hose. You don't necessarily want the vent line filling up with liquid fuel. It may make it difficult to fill with gas, at least until the liquid burps out of the vent line.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Use a vented Fuel Pump? [message #337937 is a reply to message #337933] |
Tue, 16 October 2018 19:37 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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On my early 1974 GMC there is a capped and clamped unused 3/8 barb on the left side of the rear fuel tank. This is what I used for the fuel pump return. I have an all electric fuel delivery (Carter P4070 on each tank isolated by check valves) and about 10 years ago I added a fuel return just in front of the pumps using a tee with about a .020" restriction on the return. No vapor lock even on the hottest days since that mod.
Tony S. had a 1975 GMC and it's rear tank had the same unused capped hose barb so we bought a mechanical pump with the bypass line and plumbed it to the tank. He never had any vapor lock issues after that.
I never understood why GM (amongst others) used the return line on their a/c equipped cars of the era but didn't put the return line on the vehicle that needed it the most, our GMC's. They even put a fitting on the rear fuel tank! All that was needed was a line from the fuel pump to the tank and the appropriate fuel pump from an air conditioned Toronado.
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337945 is a reply to message #337937] |
Wed, 17 October 2018 08:44 |
Dave Stragand
Messages: 307
Registered: October 2017
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Isn't that fitting on the rear tank for the Onan generator?
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Bob
Heller
Sent: Tuesday, October 16, 2018 8:37 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Use a vented Fuel Pump?
On my early 1974 GMC there is a capped and clamped unused 3/8 barb on
the left side of the rear fuel tank. This is what I used for the fuel
pump
return. I have an all electric fuel delivery (Carter P4070 on each tank
isolated by check valves) and about 10 years ago I added a fuel return
just in
front of the pumps using a tee with about a .020" restriction on the
return. No vapor lock even on the hottest days since that mod.
Tony S. had a 1975 GMC and it's rear tank had the same unused capped
hose barb so we bought a mechanical pump with the bypass line and
plumbed it to
the tank. He never had any vapor lock issues after that.
I never understood why GM (amongst others) used the return line on their
a/c equipped cars of the era but didn't put the return line on the
vehicle
that needed it the most, our GMC's. They even put a fitting on the rear
fuel tank! All that was needed was a line from the fuel pump to the tank
and
the appropriate fuel pump from an air conditioned Toronado.
--
Bob Heller
1974 X-Canyonlands 26ft
Original 455 exc for timing chain,
Rockwell intake, valve covers. 144k miles.
Winter Springs FL
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1978 Transmode (403)
Pittsburgh, PA
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337947 is a reply to message #337945] |
Wed, 17 October 2018 09:02 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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No, this fitting is in addition to the one used by the Onan. There is no dip tube attached so it would not work as a fuel supply, it is just an open (capped off) 3/8 barb about 2 inches from the top of the tank on the left side. It's accessible (barely) without dropping the tank.
I don't know if all GMC's rear gas tanks were made this way but I know of at least two that were.
Dave Stragand wrote on Wed, 17 October 2018 09:44Isn't that fitting on the rear tank for the Onan generator?
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Bob
Heller
Sent: Tuesday, October 16, 2018 8:37 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Use a vented Fuel Pump?
On my early 1974 GMC there is a capped and clamped unused 3/8 barb on
the left side of the rear fuel tank. This is what I used for the fuel
pump
return. I have an all electric fuel delivery (Carter P4070 on each tank
isolated by check valves) and about 10 years ago I added a fuel return
just in
front of the pumps using a tee with about a .020" restriction on the
return. No vapor lock even on the hottest days since that mod.
Tony S. had a 1975 GMC and it's rear tank had the same unused capped
hose barb so we bought a mechanical pump with the bypass line and
plumbed it to
the tank. He never had any vapor lock issues after that.
I never understood why GM (amongst others) used the return line on their
a/c equipped cars of the era but didn't put the return line on the
vehicle
that needed it the most, our GMC's. They even put a fitting on the rear
fuel tank! All that was needed was a line from the fuel pump to the tank
and
the appropriate fuel pump from an air conditioned Toronado.
--
Bob Heller
1974 X-Canyonlands 26ft
Original 455 exc for timing chain,
Rockwell intake, valve covers. 144k miles.
Winter Springs FL
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Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337948 is a reply to message #337947] |
Wed, 17 October 2018 09:43 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Sounds like a modification that was once popular that modified the charcoal
canister vent system. Had additional hoses connected to a shut off valve
located near the utility panel., it was used during refueling. Open the
valve to the atmosphere, and fill the tanks on high speed. When it started
to burp fuel, turn off the valve and kick off the pump. I never thought
much of that modification, but I have seen a few coaches with it. Don't
know what exactly it was supposed to accomplish, other than speed up
refueling.
Jim Hupy
Salem, Or
78 Gmc
On Wed, Oct 17, 2018, 7:03 AM Bob Heller wrote:
> No, this fitting is in addition to the one used by the Onan. There is no
> dip tube attached so it would not work as a fuel supply, it is just an open
> (capped off) 3/8 barb about 2 inches from the top of the tank on the left
> side. It's accessible (barely) without dropping the tank.
>
> I don't know if all GMC's rear gas tanks were made this way but I know of
> at least two that were.
>
>
>
> Dave Stragand wrote on Wed, 17 October 2018 09:44
>> Isn't that fitting on the rear tank for the Onan generator?
>>
>> -----Original Message-----
>> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Bob
>> Heller
>> Sent: Tuesday, October 16, 2018 8:37 PM
>> To: gmclist@list.gmcnet.org
>> Subject: Re: [GMCnet] Use a vented Fuel Pump?
>>
>> On my early 1974 GMC there is a capped and clamped unused 3/8 barb on
>> the left side of the rear fuel tank. This is what I used for the fuel
>> pump
>> return. I have an all electric fuel delivery (Carter P4070 on each tank
>> isolated by check valves) and about 10 years ago I added a fuel return
>> just in
>> front of the pumps using a tee with about a .020" restriction on the
>> return. No vapor lock even on the hottest days since that mod.
>>
>> Tony S. had a 1975 GMC and it's rear tank had the same unused capped
>> hose barb so we bought a mechanical pump with the bypass line and
>> plumbed it to
>> the tank. He never had any vapor lock issues after that.
>>
>> I never understood why GM (amongst others) used the return line on their
>> a/c equipped cars of the era but didn't put the return line on the
>> vehicle
>> that needed it the most, our GMC's. They even put a fitting on the rear
>> fuel tank! All that was needed was a line from the fuel pump to the tank
>> and
>> the appropriate fuel pump from an air conditioned Toronado.
>> --
>> Bob Heller
>> 1974 X-Canyonlands 26ft
>> Original 455 exc for timing chain,
>> Rockwell intake, valve covers. 144k miles.
>> Winter Springs FL
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> --
> Bob Heller
> 1974 X-Canyonlands 26ft
> Original 455 exc for timing chain,
> Rockwell intake, valve covers. 144k miles.
> Winter Springs FL
>
> _______________________________________________
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> Unsubscribe or Change List Options:
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337950 is a reply to message #337948] |
Wed, 17 October 2018 10:26 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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During my summers working at aircraft co I saw lot of errors we made in
engineering .
GM is no different.
On Wed, Oct 17, 2018 at 7:41 AM James Hupy wrote:
> Sounds like a modification that was once popular that modified the charcoal
> canister vent system. Had additional hoses connected to a shut off valve
> located near the utility panel., it was used during refueling. Open the
> valve to the atmosphere, and fill the tanks on high speed. When it started
> to burp fuel, turn off the valve and kick off the pump. I never thought
> much of that modification, but I have seen a few coaches with it. Don't
> know what exactly it was supposed to accomplish, other than speed up
> refueling.
> Jim Hupy
> Salem, Or
> 78 Gmc
>
> On Wed, Oct 17, 2018, 7:03 AM Bob Heller wrote:
>
>> No, this fitting is in addition to the one used by the Onan. There is no
>> dip tube attached so it would not work as a fuel supply, it is just an
> open
>> (capped off) 3/8 barb about 2 inches from the top of the tank on the left
>> side. It's accessible (barely) without dropping the tank.
>>
>> I don't know if all GMC's rear gas tanks were made this way but I know of
>> at least two that were.
>>
>>
>>
>> Dave Stragand wrote on Wed, 17 October 2018 09:44
>>> Isn't that fitting on the rear tank for the Onan generator?
>>>
>>> -----Original Message-----
>>> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of
> Bob
>>> Heller
>>> Sent: Tuesday, October 16, 2018 8:37 PM
>>> To: gmclist@list.gmcnet.org
>>> Subject: Re: [GMCnet] Use a vented Fuel Pump?
>>>
>>> On my early 1974 GMC there is a capped and clamped unused 3/8 barb on
>>> the left side of the rear fuel tank. This is what I used for the fuel
>>> pump
>>> return. I have an all electric fuel delivery (Carter P4070 on each tank
>>> isolated by check valves) and about 10 years ago I added a fuel return
>>> just in
>>> front of the pumps using a tee with about a .020" restriction on the
>>> return. No vapor lock even on the hottest days since that mod.
>>>
>>> Tony S. had a 1975 GMC and it's rear tank had the same unused capped
>>> hose barb so we bought a mechanical pump with the bypass line and
>>> plumbed it to
>>> the tank. He never had any vapor lock issues after that.
>>>
>>> I never understood why GM (amongst others) used the return line on
> their
>>> a/c equipped cars of the era but didn't put the return line on the
>>> vehicle
>>> that needed it the most, our GMC's. They even put a fitting on the rear
>>> fuel tank! All that was needed was a line from the fuel pump to the
> tank
>>> and
>>> the appropriate fuel pump from an air conditioned Toronado.
>>> --
>>> Bob Heller
>>> 1974 X-Canyonlands 26ft
>>> Original 455 exc for timing chain,
>>> Rockwell intake, valve covers. 144k miles.
>>> Winter Springs FL
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>>
>> --
>> Bob Heller
>> 1974 X-Canyonlands 26ft
>> Original 455 exc for timing chain,
>> Rockwell intake, valve covers. 144k miles.
>> Winter Springs FL
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
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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: [GMCnet] Use a vented Fuel Pump? [message #337963 is a reply to message #337947] |
Wed, 17 October 2018 21:48 |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma: -1
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Senior Member |
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[quote title=bobby5832708 wrote on Wed, 17 October 2018 08:02]No, this fitting is in addition to the one used by the Onan. There is no dip tube attached so it would not work as a fuel supply, it is just an open (capped off) 3/8 barb about 2 inches from the top of the tank on the left side. It's accessible (barely) without dropping the tank.
I don't know if all GMC's rear gas tanks were made this way but I know of at least two that were.
My early '75 Eleganza has exactly the same fitting on the rear fuel tank, about 2/3 of the way up on the left side, capped with a piece of hose and a bolt. Again, this is in addition to the Onan connection. There was no indication the tanks were ever dropped until I did it the first time about 15 years ago. That, and the similarity to Bob Heller's coach, make me think this was original GMC.
When I dropped the tanks again this year, I plumbed a return line across the front and back to this fitting, and installed a vented Toronado fuel pump. Haven't put many miles on it since, due to a battle with my gall bladder this fall, but it can't hurt. I haven't had much vapor lock for a few years, since insulating my fuel lines from the selector valve on, adding heat shields between the exhaust pipe and the tanks, and adding an auxiliary Carter pump that comes on when switching to the reserve tank. Expect this will be one more vapor lock preventer.
Rick Staples
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337972 is a reply to message #337963] |
Thu, 18 October 2018 07:25 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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Senior Member |
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Rick,
As with your GMC, back in 2006 I was the first one to drop the tanks in mine to replace the 'genuine GM' fuel lines. That's when I discovered the unused fitting on the side of the rear tank. If I remember correctly, it had a bolt and a short piece of hose capping it off. Several years later when I did the vapor bypass thing I remembered about that unused port and plumbed it up. On Tony's 1975 I think the port was capped off with a cap and clamp, although my memory isn't as good as it once was (not that it was any good to begin with).
When using a vapor bypass with a mechanical pump, the only disadvantage I can think of would be if after sitting for a while it would take longer at cranking speeds to get fuel to the carb. An electric fuel pump somewhere in the system would solve this as you could then pre-fill the carb using a low amps fuel pump rather than a high amps engine starter. On Tony's GMC he had an electric pump on the front tank that operated when the switch was in AUX so on cold starts he prefilled the carb that way. On my GMC, both tanks have their own electric pump so all I do is switch the key on, wait a few seconds, hit the pedal a couple of times, engage the starter, and in about 2 seconds the engine starts.
JWID, YMMV
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337985 is a reply to message #337939] |
Thu, 18 October 2018 15:47 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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bdub wrote on Tue, 16 October 2018 18:28Carl
How is your vapor lock solution working out? The return line with a
restrictor from the carb inlet back to the tank inlet line?
https://groups.google.com/forum/#!searchin/gmcnet-archive/carburetor$20fuel$
20return%7Csort:date/gmcnet-archive/xssYq1fQoic/Nl3ScT317DwJ
bdub
-----Original Message-----
From: Gmclist On Behalf Of Carl Stouffer
Sent: Tuesday, October 16, 2018 7:17 PM
Subject: Re: [GMCnet] Use a vented Fuel Pump?
Dave Lenzi once recommended those pumps to help combat vapor lock, but you
probably need to tap in a fitting to the filler tube for the return line
rather than the vent hose. You don't necessarily want the vent line filling
up with liquid fuel. It may make it difficult to fill with gas, at least
until the liquid burps out of the vent line.
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Billy,
It seemed to help somewhat, but didn't solve the problem altogether. I added a restrictor in the return line and that didn't seem to make a difference. I have since installed a Carter 4070 electric pump to replace the pull through pulse pump I had been running, along with a cartridge (Ford) type gas filter, and relocated the line to the OUTside of the frame. That seems to have finally done the trick. The trip we took last Summer, the coach never missed a beat in spite of several steep climbs in 90 - 100+ degree heat.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337986 is a reply to message #337985] |
Thu, 18 October 2018 16:21 |
bdub
Messages: 1578
Registered: February 2004
Location: Central Texas
Karma: 5
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Senior Member |
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Thanks Carl
Very interesting. Ya might update the photo site album with that info to
finish it out.
bdub
-----Original Message-----
From: Gmclist On Behalf Of Carl Stouffer
Sent: Thursday, October 18, 2018 3:48 PM
Subject: Re: [GMCnet] Use a vented Fuel Pump?
bdub wrote on Tue, 16 October 2018 18:28
> Carl
> How is your vapor lock solution working out? The return line with a
> restrictor from the carb inlet back to the tank inlet line?
>
>
>
> bdub
>
>
> -----Original Message-----
> From: Gmclist On Behalf Of Carl Stouffer
> Sent: Tuesday, October 16, 2018 7:17 PM
> Subject: Re: [GMCnet] Use a vented Fuel Pump?
>
> Dave Lenzi once recommended those pumps to help combat vapor lock, but you
> probably need to tap in a fitting to the filler tube for the return line
> rather than the vent hose. You don't necessarily want the vent line
filling
> up with liquid fuel. It may make it difficult to fill with gas, at least
> until the liquid burps out of the vent line.
Billy,
It seemed to help somewhat, but didn't solve the problem altogether. I
added a restrictor in the return line and that didn't seem to make a
difference. I have since installed a Carter 4070 electric pump to replace
the pull through pulse pump I had been running, along with a cartridge
(Ford) type gas filter, and relocated the line to the OUTside of the frame.
That seems to have finally done the trick. The trip we took last Summer,
the coach never missed a beat in spite of several steep climbs in 90 - 100+
degree heat.
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bdub
'76 Palm Beach/Central Texas
www.bdub.net
www.gmcmhphotos.com
www.gmcmotorhomemarketplace.com
www.gmcmhregistry.com
www.facebook.com/groups/classicgmcmotorhomes
www.facebook.com/groups/gmcmm
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| Re: [GMCnet] Use a vented Fuel Pump? [message #337990 is a reply to message #337986] |
Thu, 18 October 2018 20:16 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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bdub wrote on Thu, 18 October 2018 14:21Thanks Carl
Very interesting. Ya might update the photo site album with that info to
finish it out.
bdub
-----Original Message-----
From: Gmclist On Behalf Of Carl Stouffer
Sent: Thursday, October 18, 2018 3:48 PM
Subject: Re: [GMCnet] Use a vented Fuel Pump?
bdub wrote on Tue, 16 October 2018 18:28
> Carl
> How is your vapor lock solution working out? The return line with a
> restrictor from the carb inlet back to the tank inlet line?
>
>
>
> bdub
>
>
> -----Original Message-----
> From: Gmclist On Behalf Of Carl Stouffer
> Sent: Tuesday, October 16, 2018 7:17 PM
> Subject: Re: [GMCnet] Use a vented Fuel Pump?
>
> Dave Lenzi once recommended those pumps to help combat vapor lock, but you
> probably need to tap in a fitting to the filler tube for the return line
> rather than the vent hose. You don't necessarily want the vent line
filling
> up with liquid fuel. It may make it difficult to fill with gas, at least
> until the liquid burps out of the vent line.
Billy,
It seemed to help somewhat, but didn't solve the problem altogether. I
added a restrictor in the return line and that didn't seem to make a
difference. I have since installed a Carter 4070 electric pump to replace
the pull through pulse pump I had been running, along with a cartridge
(Ford) type gas filter, and relocated the line to the OUTside of the frame.
That seems to have finally done the trick. The trip we took last Summer,
the coach never missed a beat in spite of several steep climbs in 90 - 100+
degree heat.
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Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Good idea. I'll do that when I get a chance.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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