TheSamba.com :: View topic - Using 72 gas tank extra vent for fuel injection return

Thu May 31, 2012 10:26 pm

For some reason, my 79 fuel injected bus has a 72 gas tank in it. Since the 72 bus was not fuel injected there is no return line, so the return was tee'd into the fuel feed to the pump. The 72 has a third vent line that was plugged since there are only two vent lines in a 79. After some discussion about this on another forum topic, I decided to remove the tee and use the extra vent line as a fuel return.

Here is where I added a hole and rubber grommet for the fuel return into the gas tank compartment.

Here is what it looks where the fuel line connects to the gas tank. Also seen is a fitting to size down the fuel line. Also, you can see the wire I wrapped around the hose coming out of the tank. This was done to prevent it from kinking when bent to a 90 degree angle. Later I found you can buy a wire coil at the automotive store for just this purpose. I used some stainless steel wiring to do this.

The gas tank is silver because I used the extra POR-15 tank sealer to paint it. Ignore the bad pant job.

Here is a better look at the down sizing fitting.

This out of focus picture is from the underside of the bus showing where the fuel line comes up.

I haven't yet started the bus with this in place, but will post if I find any problems with it.

Thu May 31, 2012 10:44 pm

You should just use the Tee unless you like hearing a waterfall in
the backround 8)
And it is Dangerous too!!

you could always buy an FI tank but, many have used the tee method.

Thu May 31, 2012 11:34 pm

you should NEVER return fuel above the bottom of the tank,you aerate the fuel causing massive evaporation,far better to use the T or better yet get a Y fitting so the flow is less disturbed,or if your really keen plumb it to a swirl pot

Mon Jun 04, 2012 9:49 pm

I've heard not to use the tee. An aerospace engineering friend told me that the reason it can cause vapor lock is that when a high pressure liquid, for example the gas coming off of the gas pressure valve, mixes with a lower pressure liquid, the gas in the tank, the expanding liquid tends to produce bubbles. Of course that is theory and in practice the pressure difference might not be enough in the case of teeing the return line to the fuel pump feed.

Anyway, here is my fix to get the return line to return to the bottom (or close it) of the tank.

First off, I got some fuel line that was a snug fit into the vent line that goes into the tank. This stuff is what I found.

Here is a picture of the fuel line and the hole it will be going down. I did shorten the vent hose coming off the tank by about an inch to make things fit a little better.

Fuel line going down into the tank.

Here is a picture of the fuel line sticking out of the vent line. Not shown here is the outer hose that slips over the one I just added and clamps to the vent fitting. All is nice and snug.

Mon Jun 04, 2012 10:03 pm

You should get yourself a hunk of 30r10 submersible fuel line and use it inside the tank. The stuff you have is not designed to have continuous fuel contact on its outside sheath.

Wed Jun 06, 2012 7:16 am

Wildthings wrote: You should get yourself a hunk of 30r10 submersible fuel line and use it inside the tank. The stuff you have is not designed to have continuous fuel contact on its outside sheath.
This sounds like great advice for the next guy doing this. For me, I think I'll cut a piece of that fuel injection hose, put it in a jar of gasoline, shelf it and monitor how fast it breaks down, then replace when necessary.

I would be interested in the science behind not being designed for continuous fuel contact on the outside sheath. From close examination of the line, it is homogenous, one continuous piece of material inside and out. How then can the outside not be rated the same as the inside? It's not that I don't believe it, it's just that it seems to defy common sense.

Wed Jun 06, 2012 7:28 am

kowpeki wrote: How then can the outside not be rated the same as the inside? It's not that I don't believe it, it's just that it seems to defy common sense.
Most has an inner lining of different material that may not be visible, that said the stuff I got recently looked like it was all one unit too so it may be in some cases.

Wed Jun 06, 2012 8:02 am

just an FYI,
i was lookign for a cheap fuel filter at the FLAPS and while opening boxes to get waht I was looking for (large, cheap, clear view plastic)
one filter had a labeled Return line as well as a supply line and a output line..
this I thought would be a nice option for those in this situation as I often convert non-FI cars to Fuel injection.

I'm not sure what the code is at this moment, and if I can remember next time I'm at the flaps I'll get the code.. but just goto a (*pepboys) and open the boxes till you find one that fits my description

Wed Jun 06, 2012 8:16 am

My 85 F'nDodge van has a filter like that, the return off the filter (unfiltered side) heads back to the tank and there's a regulator on the return line down in the tank, keeps fuel flowing through the system at pressure that way. I guess it would be slightly better than a Tee but hmmm......

Sat Jun 30, 2012 1:09 pm

I'd like to revive this thread with a question. I have pulled the tank from my 72 to convert to FI and would like to put a return line in the bottom as per the FI tanks. What I am wondering is does the return line have go up into the tank above the fuel level otherwise gas will come out of that as well? Not sure if the question is clear or not. Hopefully someone will understand what I am saying. In other words what keeps the fuel from coming out of the return line?

Thanks.

Craig

Sat Jun 30, 2012 1:21 pm

Sloride wrote: I'd like to revive this thread with a question. I have pulled the tank from my 72 to convert to FI and would like to put a return line in the bottom as per the FI tanks. What I am wondering is does the return line have go up into the tank above the fuel level otherwise gas will come out of that as well? Not sure if the question is clear or not. Hopefully someone will understand what I am saying. In other words what keeps the fuel from coing out of the return line?

Thanks.

Craig

The bottom is obviously not above the fuel level. Yes fuel will run out of the return if the hose is removed. This is likely one of the main reasons FI buses burn up so easily. You might add a small check valve right at the tank to prevent fuel from back flowing out of the tank through the return.

Running the return into the top of the tank as shown earlier in this thread and then using 30r10 hose to run it to the bottom would also work and would lessen the risk of a fire consuming the whole van. This way once the return line burnt into in a fire, the back flow through the return would stop.

Sun Jul 01, 2012 4:07 am

Thanks wildthings. I'd like to try and keep the top vent pipes as they were intended. What are your thought on running the retun line on the bottom but running it as far as I can into the tank so it would be above the fuel level therefore hopefull keeping fuel from coming out of it?

Thank

Craig

Sun Jul 01, 2012 4:07 am

Thanks wildthings. I'd like to try and keep the top vent pipes as they were intended. What are your thought on running the retun line on the bottom but running it as far as I can into the tank so it would be above the fuel level therefore hopefull keeping fuel from coming out of it?

Thank

Craig

Sun Jul 01, 2012 5:29 am

Sloride wrote: Thanks wildthings. I'd like to try and keep the top vent pipes as they were intended. What are your thought on running the retun line on the bottom but running it as far as I can into the tank so it would be above the fuel level therefore hopefull keeping fuel from coming out of it?

Thank

Craig

That would mean running it up to the top of the tank internally and creating a fountain of fuel which might cause an excessive amount of fuel vapors. You want the return to be below the fuel level.

Most people adding a return line to an earlier system just "T" into the supply line before the pump.

Fri Nov 24, 2017 8:18 am

How was this issue solved?
Weighing my options to go FI on a 73 bus and exploring the return line issue.

Who has experience with the return line “T” into the supply line before the pump?

Fri Nov 24, 2017 8:23 am

I added the return line in the bottom of the tank like I mentioned. Brought it to a rad repair shop and had them braze in a line. It has been like that for 5 years without an issue.

Fri Nov 24, 2017 8:51 am

lugo2214 wrote: How was this issue solved?
Weighing my options to go FI on a 73 bus and exploring the return line issue.

Who has experience with the return line “T” into the supply line before the pump?

I do. On some other systems like D-jet when replacing the original pump with a much larger two port pump like a Bosch 044 ..... It has some merit.....but only if your pump has some difficulty with self priming like an 044.

The original system already had a suppply outlet from the tank to the filter and pump and a return inlet from the ring main to the bottom of the tank. Since the D-jet were originally three port pumps.....the return/relief valve from the pump would tee into the return line from the injectors and feed into the tank.

When putting in a two port pump.....like the 044.....it really helped feeding to leave the tee....actually a "Y" in place.....and add another tee.....actually a "Y" ....into the tank outlet feeding the pump.....to actually cross connect the return line from the injectors to the inlet line for the pump. This helped to prevent cavitation.

Its not necessary on normal low preszurd L-jet pumps.....but can be a fine method for allowing to use a fuel injection system on with a nin fuel iniection single outlet tank.

But...you must use a "Y" and not a tee. A tee entrance to a line with fuel in motion causea turbulence that can cause cavitation. Ray

Fri Nov 24, 2017 9:55 am

Thank you both for the reply

Are there any pics of both the Y connector or the bottom braided inlet?

Fri Nov 24, 2017 10:43 am

lugo2214 wrote: Thank you both for the reply

Are there any pics of both the Y connector or the bottom braided inlet?

Give me a few to dig them out. In the past I have made diagrams in for:

1.L-jet stock
2. D-jet stock which is 3 port and shows the return line from the pump "Y"'d into the return line from the tank for reference.....and is important because it tells you the proper orienaltation of the "Y"

3. Going from D-jet to a two port L-jet style pump....and the return line cross connect

4. L-jet or any system using a two port pump with a single port carburettor tank and a feeder "Y".

I am driving for about two hours then I can sit,down and pull up the diagrams. Ray

Fri Nov 24, 2017 10:46 am

Awesome thank you