[GMCnet] Fuel system.

[John Phillips]

Hi,
I have a 75 Avion built on a 74 chassis.
The fuel line from the fuel pump to the carburetor has a hose connecting 2
sections of the line. There are about 2 inches of space between the 2 ends,
the ends look like they are factory cuts rather than someone just cut 2
inches out of the line. I have been told there should not be any hose after
the pump.

I parked in my driveway 4 days ago with the front wheels about 8 inches
higher than the back wheels.
The engine has taken several seconds to start if it has not run for a day
or 2.
When I took the line apart I was surprised there was no fuel leakage. There
is a clear fuel filter at the pump input with just a little fuel in it.

What should keep the fuel from running back into the tank so the fuel pump
does not have to charge the line?

Did the 74 units come with a solid line from the pump to the carburetor?

One good thing is the oil pump has time to lube the engine before it starts

--

*John Phillips*
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[John Wright]

John,

The Avion was build in 1975 only, some of the pieces may have come from the very last of the 74 parts that were left over making your 75 a very early Avion. Your VIN Chassis identification should be TZE 365 V 10XXXX were the last digits are your chassis number. I also own a 75 Avion that is in the process of a frame up restoration, hope to finish it next year.

As from the factory there should be NO rubber on top of the engine on the fuel line that runs from the fuel pump to the carb! That is a safety hazard and could result in you losing your coach to a fire. The 2 options available are the hard metal line.

http://www.appliedgmc.com/prod.itml/icOid/918

Or the flexible steel braided line with the fire shield jacketing.

http://www.appliedgmc.com/prod.itml/icOid/853

The fact that it takes several seconds to get the enough fuel into the carb is typical. The fuel typically evaporates out of the carb when the engine is warm and then sits for any period of time. Many have added an electric fuel pump back near the selector valve to prime the pump if the coach has been sitting and some have gone to all electric fuel systems eliminating the mechanical pump altogether. This is one way to go or you can build your own.

http://www.appliedgmc.com/prod.itml/icOid/1790

This layout of the electric fuel pump allows you to still use the mechanical fuel pump.

Another change I would suggest in your fuel system is do not use a plastic fuel filter anywhere in your fuel system. The following would be much better and safer. I did use 2 filters in my system, one in the back before the pump and one up front located at the former mechanical fuel pump location feeding the metal line to the carb.

http://www.appliedgmc.com/prod.itml/icOid/1636

Or find one locally that is a 3/8” in and out.

JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan

[John Phillips]

My chassis VIN is TZE064V101164 and the Avion VIN is A26000 and it has an
Edelbrock air cleaner.
The main thing is how do I keep gas in the filters and fuel lines. I do
plan on replacing the hose part from the fuel pump to the carb. I would
like a pressure tap in there some place.

Is there a check valve in the pump?
Would an air leak between the carburetor and the pump cause the bleed down?

After I get the fuel bleed down problem fixed I plan on installing a Wix
33161 but I do not want to crank the engine long enough to fill that large
filter.

[Ken Burton]

I do not think the fuel is bleeding down throught the fuel pump. The fuel is evaporating in the float bowl of the carb. This is due to the high
temperature of the exhaust crossover under the carb. The solution is to block the intake manifold exhaust crossover. Kits to block the crossover are
available from Dick Paterson at Springfield Ignition or Jim Kanomata at Applied GMC.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

[John Phillips]

If that is case ken how do you explain why they fuel line from the
carburetor to pump was empty as well as the fuel filter below the pump?
I parked there Tuesday afternoon and this morning I took the fuel line off.

--

*John Phillips*

[Rob Mueller]

John,

I have pasted all three of your emails below and have interspersed comments in CAPS below for clarity - I'm not shouting.

As you can see from my signature I have two Avions.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of John Phillips
Sent: Saturday, September 9, 2017 1:02 PM
To: gmc...@list.gmcnet.org
Subject: [GMCnet] Fuel system.

Hi,

I have a 75 Avion built on a 74 chassis.

BOTH OF MY AVIONS WERE BUILT IN 1974; ONE IN OCTOBER ONE IN NOVEMBER.

The fuel line from the fuel pump to the carburetor has a hose connecting 2 sections of the line. There are about 2 inches of space
between the 2 ends, the ends look like they are factory cuts rather than someone just cut 2
inches out of the line. I have been told there should not be any hose after the pump.

ALL GMC'S NO MATTER THE OUTFITTER (AVION, COACHMAN, MIDAS, ETC) ALL CAME WITH A METAL LINE FROM THE OUTLET OF THE MECHANICAL FUEL
PUMP TO THE CARB. IF IT'S NOT METAL IT'S NOT OEM.

I parked in my driveway 4 days ago with the front wheels about 8 inches higher than the back wheels. The engine has taken several
seconds to start if it has not run for a day or 2. When I took the line apart I was surprised there was no fuel leakage. There is a
clear fuel filter at the pump input with just a little fuel in it.

IT IS POSSIBLE THAT FUEL SIPHONED BACK INTO THE FUEL TANK.

What should keep the fuel from running back into the tank so the fuel pump does not have to charge the line?

NOTHING, THE FUEL CAN'T DRAIN OUT OF THE FUEL BOWL AND ONCE IT STARTS THE FUEL PUMP CHARGES IT IMMEDIATELY.

Did the 74 units come with a solid line from the pump to the carburetor?

YES AS NOTED ABOVE.

One good thing is the oil pump has time to lube the engine before it starts

YEP!

*John Phillips*

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of John Phillips
Sent: Saturday, September 9, 2017 5:59 PM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Fuel system.

My chassis VIN is TZE064V101164 and the Avion VIN is A26000 and it has an Edelbrock air cleaner.

BOTH MY AVIONS WERE BUILT BEFORE YOURS

The main thing is how do I keep gas in the filters and fuel lines.

DOESN'T MATTER SEE ABOVE.

I do plan on replacing the hose part from the fuel pump to the carb. I would like a pressure tap in there some place.

THE CONNECTION FROM THE FUEL PUMP TO THE Q-JET SHOULD BE A SOLID METAL LINE NOT RUBBER. IF IT'S RUBBER IT'S NOT OEM. I WOULD SUGGEST
YOU REPLACE IT WITH ONE OF THESE AS THEY ARE MUCH EASIER TO REMOVE AND INSTALL THAN THE SOLID METAL LINE.

http://www.appliedgmc.com/prod.itml/icOid/853

IN MY OPINION THERE IS NOTHING TO BE GAINED BY PUTTING A PRESSURE TAP IN. I HAVE PUT 80,000 MILES PLUS ON DOUBLE TROUBLE AND NOT HAD
ANY NEED TO CHECK THE FUEL PRESSURE.

Is there a check valve in the pump?

I DON'T KNOW.

Would an air leak between the carburetor and the pump cause the bleed down?

POSSIBLY BUT IT WOULD PROBABLY LEAK FUEL WHEN THE ENGINE WAS RUNNING.

After I get the fuel bleed down problem fixed I plan on installing a Wix 33161 but I do not want to crank the engine long enough to
fill that large filter.

IF YOU HAVE DROPPED AND CLEANED YOUR FUEL TANKS AND REPLACED THE FUEL LINES WITH ETHANOL COMPATIBLE LINES YOU DON'T NEED A LARGE
FILTER HERE'S WHAT IS INSTALLED IN BOTH MY AVIONS:

http://www.gmcmhphotos.com/photos/aa-miscellaneous-photos/p54750-fuel-pump-inlet-filter.html

*John Phillips*

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of John Phillips
Sent: Sunday, September 10, 2017 1:07 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Fuel system.

If that is case ken how do you explain why they fuel line from the carburetor to pump was empty as well as the fuel filter below the
pump?

DOESN'T MATTER AS THE FUEL CAN'T DRAIN OUT OF THE FUEL BOWLS WHICH IS INDICATED BY YOU NOTING IT ONLY TOO COUPLE OF SECONDS FOR THE
ENGINE TO START, ONCE THE ENGINE STARTS THE FUEL PUMP SUCKS FUEL OUT OF THE TANKS AND REFILLS THE BOWLS.

I parked there Tuesday afternoon and this morning I took the fuel line off.

[Johnny Bridges via Gmclist]

For what it's worth, the outlet valve in the fuel pump is essentially a check valve. A diaphragm pump won't work without it.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

[Matt Colie]

Johnny Bridges wrote on Sun, 10 September 2017 08:58

> For what it's worth, the outlet valve in the fuel pump is essentially a check valve. A diaphragm pump won't work without it.
>
> --johnny

Close Johnny,

Both the Inlet and the Outlet valves have to be check valves, so both would have to leaks to let the fuel run back.
But, if you sucked up rust from the tanks, I suppose it could happen.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[Johnny Bridges via Gmclist]

Have a look http://www.gmcmhphotos.com/photos/cane-9-creek-rv-park-heflin-2c-al/p58462-fuel-pump-follies.html and the next 3 or 4 photos. One of the
check valves has busted a part of the seal which was hardened from alcohol gas. The diaphragm is ready to go as well. And the housing is beginning
to rust. Weird symptoms from that one.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

[Johnny Bridges via Gmclist]

I'm hip. But he was asking about a check valve - there's two.

--johnny

--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

[John Phillips]

Thanks for the info. Next question is, do I go electric or replace with the
original? The 2 pump electric looks good in that there is some redundancy
but there is hose after the pump. Is that ok here but not in the front of
the engine? The open relay contacts are not wither proof.

On Sun, Sep 10, 2017 at 9:27 AM, Johnny Bridges via Gmclist <
gmc...@list.gmcnet.org> wrote:

> Have a look http://www.gmcmhphotos.com/photos/cane-9-creek-rv-park-

--

*John Phillips*

[Matt Colie]

johnd01 wrote on Sun, 10 September 2017 16:25

> Thanks for the info. Next question is, do I go electric or replace with the
> original? The 2 pump electric looks good in that there is some redundancy
> but there is hose after the pump. Is that ok here but not in the front of
> the engine? The open relay contacts are not wither proof.

> --
> *John Phillips*

John,

It will be nearly impossible to assemble a GMC fuel system with no rubber in the pressurized part of the system. The caution is to not have rubber on
top of the engine where if it <Three Phone Calls> should leak, it can pool on top of the hot engine. If it leaks on the ground, nobody but the EPA
and the gut that has to patch the McAdam will care.

Matt <finally>

--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[John Phillips]

I have 2 inches of pipe coming from the fuel pump followed by 6 inches of
hose bridging a 2-inch gap in the tubing ending about an inch before the
bend to over the intake manifold. I have been told I need to replace the
line with a solid tube.
I have also been told to replace the clear plastic fuel filter just below
the pump.
Do I really need to?

--

*John Phillips*

[Johnny Bridges via Gmclist]

'Do I really need to?' Well, it's your chooice. Do you want to reduce the chances of the coach catching fire?It's up to you.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

[Rob Mueller]

Johnny,

Spot on Mate!

I forgot to point John to this document:

http://www.gmceast.com/technical/Mueller_GMCer-Fire-Guide.pdf

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Johnny Bridges via Gmclist
Sent: Monday, September 11, 2017 7:44 AM
To: gmc...@list.gmcnet.org
Cc: Johnny Bridges
Subject: Re: [GMCnet] Fuel system.

[Richard Denney]

The engine compartment is very hot, and hoses are vulnerable to heat. But
the main problem is that if it does leak (and all rubber hoses leak
eventually unless they are replaced frequently), it spreads fuel over very
hot surfaces with a high probability of ignition.

I confess that I use a hose from my solid line down at the frame
crossmember to the carb inlet, but it is high-temp aircraft-grade hose with
AN-6 fittings. I would never use a plain rubber fuel hose over the top of
the engine.

As to the plastic fuel filters, even moreso. Just below the pump is quite
close to the exhaust manifold, and you do not want to spray fuel onto that.
The FRAM G-15 filters are in steel cans and they are easy to get and easy
to install.

Rick "bending a steel line to avoid that thermostat housing, however,
requires real skills" Denney

On Sun, Sep 10, 2017 at 6:05 PM, John Phillips <john.ph...@gmail.com>
wrote:

> I have 2 inches of pipe coming from the fuel pump followed by 6 inches of
> hose bridging a 2-inch gap in the tubing ending about an inch before the
> bend to over the intake manifold. I have been told I need to replace the
> line with a solid tube.
> I have also been told to replace the clear plastic fuel filter just below
> the pump.
> Do I really need to?
>
>

--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com