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Old 05-18-2019, 06:08 PM   #1
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Replacing my gas lines.

While working on my 345 I noticed a leak in a gas line near the gas tank.
I was intending to replace them anyway but this makes it a top priority.


What is the best line to use and how much do i need?
I see that you can get nylon reinforced hose which is like the original.
You can also get stainless armored for more money. Some hoses are
not for E85 gas. Does this matter? I can imagine that the stainless
hose must be hard to work with. How do you cut it? Are the cut
ends really sharp? Would a 50 foot roll be enough?


I have looked at the discussion about replacing the hoses on the top
of the tank. You must either drop the tank or cut a hole in the
floor. I am inclined to cut the hole.


Any other thoughts or advice?
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Old 05-20-2019, 09:48 AM   #2
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I would also be inclined to cut a hole, if for no reason other than easy access later

The engine is not compatible with E85, but I might go for hose that is. They keep wanting to add more of that crap to gas.

If you don't already have an automatic shutoff for the electric fuel pump, now is a good time to add one.
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Old 05-20-2019, 10:26 AM   #3
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Automatic fuel pump shutoff? What is that?
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Old 05-20-2019, 04:17 PM   #4
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If you are going to pull the fuel tank out.....and cut a hole, screw the rubber lines and put steel in. 3/8” for the engine, 5/16” for the generator. You can keep the 3/8” vent line rubber. Regards, Bob
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Old 05-20-2019, 07:46 PM   #5
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Fuel line jumps to 1/2 and than to a steel line outside of the frame to a inertia fuel shutoff ball. It looks like a filter.
I would pull the tank and look for rust under the straps good spot for a leak. Hope you got skinny hands to get in the frame area by the rear end and tag axle.
I have the same year and the fuel hose was junk when I did the work. When you take the tank out you can look inside to see if things are good or bad.
Don't forget the filler neck hose I think you can get to one of the hoses in the bedroom.
Up at the fuel pump is a snake looking hose can't get that anymore so make a loop.
All this was done before the body was put on the frame at airstream so things are just long enough but not long enough when I had to do it.
If you can get the MO up in the air some it helps.
And I added a new electric fuel pump with a clear filter before the electric pump. It's a pain in the butt but has to be done. Enjoy. My shoulder stopped hurting a year later.
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Old 05-21-2019, 06:12 PM   #6
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I can't get it up in the air too much. I will depend on the levelers
and jacks. Mostly I will be doing it on my back.


This is not a return flow system like modern cars I assume.
I remember in the old days having problems with vapor lock on
hot days in my car. Has anyone modified the system to add a

return flow?
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Old 05-22-2019, 04:49 AM   #7
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Don't know if this will help but this is the top of the tank on my 1991 350. It does have fuel injection so there is a return line there.
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Old 05-22-2019, 05:44 AM   #8
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This is a good example of slang terms causing confusion. Gas is a vapor and most folks here think of LP when the word gas is used. OP is obviously referring to gasoline:-) "Fuel line" might be more clear.
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Old 05-22-2019, 06:40 AM   #9
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Quote:
Originally Posted by BambiTex View Post
This is a good example of slang terms causing confusion. Gas is a vapor and most folks here think of LP when the word gas is used. OP is obviously referring to gasoline:-) "Fuel line" might be more clear.
I guess that depends on which forum you're in. Being this was posted in the motorhome section I assumed he was talking about the "gas lines" from the gas tank to the engine.
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Old 05-22-2019, 08:26 AM   #10
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Maybe that’s why you’re in a trailer......Regards, Bob
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Old 05-22-2019, 09:45 AM   #11
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Yes, gas line = gasoline line. Vapor lock is the problem caused
by gasoline boiling in the lines on a hot engine on a hot day causing
the engine to stop.



The return flow systems in cars today eliminate this problem
by continually circulating the gas through the lines back to
the gas tank. This keeps the gas in the loop cool.



My 1972 boat had vapor lock problems on hot days. I added
a return line to the tank with a valve in that line to restrict
the flow. I could adjust it to maintaine enough pressure to

the carburetor. No problem now.


While I am swapping out the gas lines it would not be too much
additional work to add a gasoline return line. Is it worth it? Do

these motorhomes have a vapor lock problem?
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Old 05-22-2019, 10:02 AM   #12
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I thought most of these motorhomes had return lines built in. Maybe I'm mistaken though. I have one but I don't know if it was original. At least I think I have one... now I'm gonna go check.
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Old 05-22-2019, 10:55 AM   #13
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Quote:
Originally Posted by Magnet18 View Post
I thought most of these motorhomes had return lines built in. Maybe I'm mistaken though. I have one but I don't know if it was original. At least I think I have one... now I'm gonna go check.
They do come from the factory with return lines. The feed line is 1/2" and the return line is either 3/8" or 5/16". I believe the 1/2" line changes to 3/8" when it hits the mechanical gas pump. From the pump the carburetor it should be 3/8".
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Old 05-27-2019, 07:42 PM   #14
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I started my project by cutting through the floor under the bed.
I measured from the edge of the rear right side storage locker
to get the best position to cut the opening. I ended up being
a little off but close enough.

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After cutting all the way around, the wood panel would not come out.
It seems that they pounded a hardened nail through the wood into
the steel cross member.

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I used a hole saw to cut around the nail. Then i could pull the
panel out.

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After getting it all opened here is what I saw. The mice have
made this home for a while.

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This is a close-up of the hose connections.

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Two hoses go to the left in this picture (actually the right side of
the motorhome) and two go the the right. One of the hoses that
go to the left is the one that leaks. I can't get to the leaky hose
yet since it it near the top corner of the tank.

You can see that one hose has a large gash in it but it does not
seem to leak. The hoses seem to be 3/8" and 5/16". I ordered
two spools of Gates "Barricade" fuel line. That is supposed to be
good for any type of gas or ethanol.

The one that goes straight to the left is pulled so tight that it
seems to be kinked at the fitting into the tank.

I don't know which lines are for the engine or the generator
or the vent or the return line. I will find out when I begin
pulling the new lines.

I read on the internet (only be truth there!) that ordinary gas
like passes one gallon of gas per year by permeation in an average
car. This Gates product looses less that a table spoon of gas.

I don't want to remove the sender unit to look into the tank
for rust because the tank is half full. It does not look rusty on the
outside so I am hoping for the best.

When the new hose arrives I will continue.
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Old 08-04-2020, 06:21 PM   #15
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Quote:
Originally Posted by bkahler View Post
They do come from the factory with return lines. The feed line is 1/2" and the return line is either 3/8" or 5/16". I believe the 1/2" line changes to 3/8" when it hits the mechanical gas pump. From the pump the carburetor it should be 3/8".
I just replaced all my fuel lines, and I'm wondering if I should be figuring out how to install a return line. I'm not sure if my 1975 Argosy never had one, or if the previous owner removed it.

My sender unit has three metal ports.



In this photo, the bottom one goes to the motor (it connects to a 5/16" hard line next to the tank). The top one goes to the Onan (and is 3/8" rubber pretty much the whole way). The third is either a vent or a return. You can see there was a four inch piece of 3/8" fuel hose hooked up to the middle port, but it was blocked with a solid, semi-clear gunk (it's sticking part was out in the photo). It looked like yellowed silicon. I assume it was gelled "something," but I have no way of knowing if the previous owner snipped it when it became blocked, or if that stuff "grew" while it was functioning as a vent.

There are vent hoses on either end of the tank that go up to the filler neck, so it doesn't seem like that third port would be a vent.

If that middle port should be a return, from what location (where on the motor) would I be returning the fuel? Is there a return port on the carb I should be looking for?
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Old 08-04-2020, 07:00 PM   #16
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Hey.
Use high pressure fuel injection gas line . Its thicker designed for our gas of today. And if you decide to go with aftermarket fuel injection. All you got to do is splice in the pumps filters etc etc. You won t have to pull the fuel tank . All your lines will be new .
Also don't forget the fuel line at the fuel pump on the motor. And the 1/4 return line off the engine fuel pump. That's the line that gets hot an brittle.
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Old 08-04-2020, 09:24 PM   #17
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Thanks for the heads up, but the fuel lines have already been replaced. My question was about a return line (do I need to reintroduce one to a system that hasn't been using one for who knows how long, and if so, where up at the motor does it attach).
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Old 08-05-2020, 05:02 AM   #18
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Thanks for the heads up, but the fuel lines have already been replaced. My question was about a return line (do I need to reintroduce one to a system that hasn't been using one for who knows how long, and if so, where up at the motor does it attach).
I believe you definitely want a return line. I've worked on a half dozen of these rigs now and all of them had the return line. If you are still using the mechanical fuel pump along with your P4070 you'll need to make sure the fuel pump has the return line fitting. If it doesn't I would recommend replacing the pump and running a 5/16" return line.

There are a couple versions of the mechanical pump. Some GM vehicles did not use a return line but used the same pump so GM only used the 3/8" suction line. Your pump should have 5/16" and 3/8" tubes on it.

As suggested if you do eventually install efi you'll need the return line.
Brad
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Old 08-05-2020, 03:54 PM   #19
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I believe you definitely want a return line. I've worked on a half dozen of these rigs now and all of them had the return line. If you are still using the mechanical fuel pump along with your P4070 you'll need to make sure the fuel pump has the return line fitting. If it doesn't I would recommend replacing the pump and running a 5/16" return line.

There are a couple versions of the mechanical pump. Some GM vehicles did not use a return line but used the same pump so GM only used the 3/8" suction line. Your pump should have 5/16" and 3/8" tubes on it.
Thanks, Brad. The previous owner removed the mechanical pump, so the Carter is the only pump in the fuel line. I put the new in-tank strainer (sock) on the sender uptake today, and poured in two gallons of new gas. This thing runs like a top. I'm kind of surprised by how quietly it idles.

So I still need to figure out this return line thing. It "works" without it, and evidently did for the previous owner as well, but it seems like a return line is still a good idea.
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Old 08-05-2020, 04:06 PM   #20
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Thanks, Brad. The previous owner removed the mechanical pump, so the Carter is the only pump in the fuel line. I put the new in-tank strainer (sock) on the sender uptake today, and poured in two gallons of new gas. This thing runs like a top. I'm kind of surprised by how quietly it idles.

So I still need to figure out this return line thing. It "works" without it, and evidently did for the previous owner as well, but it seems like a return line is still a good idea.
Some research is needed but I believe one of the issues with no return line is the fuel gets hotter prior to entering the carburetor. That may not be a problem on some vehicles but these rigs run hot to begin with so having hot fuel certainly doesn't help matters any. I think I read this somewhere but I have no idea where

Brad
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