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Gas Tank Fuel Hose Routing 1973 Fastback
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Scorpion1110
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PostPosted: Sun Jun 13, 2021 6:55 pm    Post subject: Gas Tank Fuel Hose Routing 1973 Fastback Reply with quote

Interesting perspective on the Type 3 this afternoon. I spent a couple of hours with my nose in the Bentley Manual while doing web searches to identify the right fuel hose layout in the Type 3.

I pulled the gas tank to check fuel hoses, and begin replacement with Ethanol compatible hose and FI clamps. When I pulled the tank the first thing I noticed on the fuel hose was "Not for Fuel Injection". OK. The next thing I notice is one of those little in-line glass fuel filters. The ones that can crack and throw fuel everywhere. OK again.

So I give everything a hard look;

The factory pump has 3 ports S -suction, D - pressure, R - return.

In my fastback currently, the R-port goes to the L-shaped fitting on the fuel tank and shows the label in my pic. The S-port is running to the straight outlet under the fuel tank and runs through the square filter, and the D port is running to the rear line through the tunnel on the driver side with the glass inline filter.

Did the PO set get this right? I haven't found a definitive diagram. I did notice the FI square filter on top of the pump so that's correct.

I have attached a few pics. I just want to confirm the plumbing before I start replacing hose and pulling that darn glass filter.

Here is the Bentley pic

Image may have been reduced in size. Click image to view fullscreen.


Here is a pic of what I am looking at:

Image may have been reduced in size. Click image to view fullscreen.


Thanks for your help!

Dave
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raygreenwood
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PostPosted: Sun Jun 13, 2021 8:54 pm    Post subject: Re: Gas Tank Fuel Hose Routing 1973 Fastback Reply with quote

The glass inline filter....SHOULD be a strainer only...like a 100um strainer. Putting it upstream of the square fuel filter or the fuel pump...is worthless.

Its function is as a "rock/sand" filter. It goes between the fuel tank ...and the square filter....and ALWAYS goes BEFORE the pump. The function is to keep sand out of the filter so it does not wear holes through the pleated paper....because if sand gets to the pump....it will kill it.

The square fuel filter should be 20 microns or less. Depending on brand it could be down to 10 microns but I doubt it. Its typically 15-20...but I can check the spec.

In the old days...I think it changed first around the early 90's...the square cube filters had a packed "lint" pre-filter before the pleated filter. This was a backup...for the 100-150 micron sock type sand filter inside of the fuel tank on the inlet pipe to the fuel pump.

When you started seeing the translucent white filters...mostly made in Israel....for a few years they still had the square pleated filter block inside. At some point...they are all now a round cartridge filter inside. There is no reason why these even have to be square anymore.

If you do not know what micron level the glass filter is....then take it out. It does not belong upstream of the pump either way.

Those glass filters are excellent.....as Pre-filters..... for the main square filter. This allows you to get that pain in the ass sock filter out of the tank...and just use the glass pre-filter to do that job.

You can check out my write up one of those glass filters here. You would be hard pressed to break one one unless you are over about 50 psi...or beating on it....or have it poorly installed....but either way if you are using it....it should only be on the inlet/low pressure side.

https://www.thesamba.com/vw/forum/viewtopic.php?p=9594363&highlight=#9594363

Ray
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Scorpion1110
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PostPosted: Mon Jun 14, 2021 4:17 am    Post subject: Re: Gas Tank Fuel Hose Routing 1973 Fastback Reply with quote

Ray;

Thank you for the write-up and explanation on the filters. I agree.

I built a feisty 55 Chevy wagon and had a 100micron coming out of the tank with a fuel cutoff, and then a 35 micron with a check valve at the carb (check valve to keep fuel up to avoid hard starts) It was a 2 quad SBC, and I used nearly your same suggested set-up.

With the Type3, I am trying to avoid assumptions since the engineering seems simple but specific. So this is very useful Smile

Did you have any thoughts on the lines or plumbing arrangement? I am unsure of the pump ports and where they should be plumbed.

I am still wrestling with the reasoning as well as trying to make sure the plumbing is on spec. Based on some info that Ive read a 2-port pump seems easier- at least for me conceptually Smile

I really appreciate your help. I always try to research through the web and this site before I use up forum space or member time.

Thanks again, Dave
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raygreenwood
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PostPosted: Mon Jun 14, 2021 6:57 am    Post subject: Re: Gas Tank Fuel Hose Routing 1973 Fastback Reply with quote

Scorpion1110 wrote:
Ray;

Thank you for the write-up and explanation on the filters. I agree.

I built a feisty 55 Chevy wagon and had a 100micron coming out of the tank with a fuel cutoff, and then a 35 micron with a check valve at the carb (check valve to keep fuel up to avoid hard starts) It was a 2 quad SBC, and I used nearly your same suggested set-up.

With the Type3, I am trying to avoid assumptions since the engineering seems simple but specific. So this is very useful Smile

Did you have any thoughts on the lines or plumbing arrangement? I am unsure of the pump ports and where they should be plumbed.

I am still wrestling with the reasoning as well as trying to make sure the plumbing is on spec. Based on some info that Ive read a 2-port pump seems easier- at least for me conceptually Smile

I really appreciate your help. I always try to research through the web and this site before I use up forum space or member time.

Thanks again, Dave


The three ports:

S= suction/inlet.....the fuel hose route: fuel tank>>>>> square filter>>>>>>pump

D= discharge/output..... the fuel hose route: pump/D-port >>>>>> inline anti-harmonic chamber>>>>metal line from tunnel on left side of car for type 3 (check me on this one. My car/412 runs ipposite with regulator on left side)

R= return/bypass.....the fuel hose route: pump/R-port >>>>>>> "Y" fitting right leg>>>>>fuel tank return connected to forward facing leg of the "Y"fitting >>>>>>left leg of "Y" connected to return line drom regulator

Ray
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raygreenwood
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PostPosted: Mon Jun 14, 2021 10:35 am    Post subject: Re: Gas Tank Fuel Hose Routing 1973 Fastback Reply with quote

So I have posted these before but here is a little more detail:

This is the type 3 specific- three port pump system layout:

Image may have been reduced in size. Click image to view fullscreen.


Here is type 3 specific with an aftermarket 2 port pump

Image may have been reduced in size. Click image to view fullscreen.


Ray
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Scorpion1110
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PostPosted: Mon Jun 14, 2021 11:16 am    Post subject: Re: Gas Tank Fuel Hose Routing 1973 Fastback Reply with quote

Ray-

This is perfect! Makes sense. You just made me Type 3 smarter.

Many thanks- time to plumb.

Dave
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