Opel GT Forum banner
1 - 11 of 11 Posts

·
Opeler
Joined
·
18 Posts
Discussion Starter · #1 ·
Hello, I've had my 73 GT for many years, but it has been stored for a long time with a bone dry gas tank.

I have been using an auxiliary fuel tank with electric pump so that I can start the engine periodically without having to deal with keeping fuel fresh in the original gas tank.

I am now starting to make it roadworthy again, and one item on my to do list is to replace all of the original tank vent lines and possibly fuel supply lines, so I can hook up and use the original gas tank again.

After reading most of the vent line threads on this site, I am a bit confused about whether the fuel return line from the second outlet on the fuel filter is supposed to return liquid or vapor to the gas tank.

The last time I ran this 73 GT using its original fuel system, I noticed that gas was dripping from the area around the gas tank rubber grommet, but it would only drip if the engine was running. I put off doing anything at the time since I was going to store the car. Do you think this issue was due to a cracked return line leaking liquid fuel from its tank fitting? Could this also have been due to an incorrect fuel filter placement in a horizontal position such that liquid, rather than vapor, flowed through the return line back to the tank?

I am curious about this problem as I have not worked on carburetted cars for a long time, and I always thought the function of a fuel return line was to return surplus (liquid) fuel to the tank rather than vapor?
 

·
Über Genius
Joined
·
9,401 Posts
The short answer is it does both.
The 73 had a pressure correcting filter on it that allowed the fuel pump to run "free" without building up pressure against the float valve. AND it also prevented vapor lock, allowing built up fuel vapors to be eliminated via the return line, AND when the car was shut down, excessive vapors could also be sent to the tank.
 

·
Registered
Joined
·
11,747 Posts
...

The last time I ran this 73 GT using its original fuel system, I noticed that gas was dripping from the area around the gas tank rubber grommet, but it would only drip if the engine was running. I put off doing anything at the time since I was going to store the car. Do you think this issue was due to a cracked return line leaking liquid fuel from its tank fitting?
Raw fuel leakage is never a GOOD thing IMO.
 

·
Opeler
Joined
·
18 Posts
Discussion Starter · #4 ·
Thanks, First opel 1981 for your explanation. That makes sense why it only leaked when the engine was running; I was wondering how a fuel filter could tell the difference between gas and vapor. I guess the downside of the 73's extra return line is that a fuel leak can occur in both directions as the plastic ages.

And thanks wrench459 for your concern, the original tank and lines have been drained and dry for many years after this issue was noticed and the car has been stored in a well ventilated space. The vent and gas lines will be replaced before putting gas in the original tank.

Tom
 

·
Registered
Joined
·
11,747 Posts
Chuckle:
Yeah those three port fuel filters are a bitch.
I remember having to replace 318 Mo-Poops in the correct location.

Funny thing if you didnt use the included new shorty fuel hoses
the carb could ingest a old piece of rubber
:D
 

·
Registered
Joined
·
191 Posts
Bumping this old thread.

I've been experiencing vapor lock on my 73 GT. It has the 3 port fuel filter with the return line to the tank and has the stock mechanical fuel pump.

This may be a stupid question, but should the return line from the fuel filter to the tank be fairly unrestricted? I assume it should be. I removed the hose and attempted to blow into the line to see if vapor/air could move freely, but the line is very restricted and it doesn't seem that air can pass through it. I took off the gas cap and that didn't make any difference.

I did find a gas station that sells ethanol-free fuel close by to me, so I'm going to get a tank of that later today.
 

·
Registered
Joined
·
983 Posts
Bumping this old thread.

I've been experiencing vapor lock on my 73 GT. It has the 3 port fuel filter with the return line to the tank and has the stock mechanical fuel pump.

This may be a stupid question, but should the return line from the fuel filter to the tank be fairly unrestricted? I assume it should be. I removed the hose and attempted to blow into the line to see if vapor/air could move freely, but the line is very restricted and it doesn't seem that air can pass through it. I took off the gas cap and that didn't make any difference.

I did find a gas station that sells ethanol-free fuel close by to me, so I'm going to get a tank of that later today.
My understanding is that the fitting at the tank has a reduced size orfice. That’s where I suspect you might have a restriction. You may want to manually clear that out, rust or build up could have blocked it. Just trace the line back to the tank,
 

·
Super Moderator
Joined
·
5,947 Posts
My understanding is that the fitting at the tank has a reduced size orfice. That’s where I suspect you might have a restriction. You may want to manually clear that out, rust or build up could have blocked it. Just trace the line back to the tank,
I happen to have a '73 GT gas tank on hand (first I have ever really looked at). The "vapour return line" from the filter connects to the smaller of the two lines, shown in the attached photos, at the driver's side rear corner of the tank. The vent line connection next to it, and the vent line connection at the front passenger side corner, both have restriction orifices in the nozzles.

The fuel vapour return line connection does NOT have a restriction orifice.
 

Attachments

·
Opel Rallier since 1977
Joined
·
2,278 Posts
I do think it is correct that the return is open. Makes no sense otherwise. May be time for a bit compressed air blown with gradually increase flow/pressure through that return line. Sometimes those lines take some odd twists in turns inside the tanks; there is always a concern of them becoming gas leaks in an overturned car in a wreck, so they sometimes get contorted in a way to limit that. (Which is why any tank vapor lines go through all their contorted connections before they go to the carbon canister in engine compartment.)
 

·
Registered
Joined
·
191 Posts
Thanks for the replies. I'll pop that connection off the tank and check that both the hose and tank connection are clear and open. I haven't had the tank out, but did drop a camera in it to look around when replacing the fuel sender gaskets and vent lines last year and it looked to be in good shape then.
 

·
Registered
Joined
·
78 Posts
I happen to have a '73 GT gas tank on hand (first I have ever really looked at). The "vapour return line" from the filter connects to the smaller of the two lines, shown in the attached photos, at the driver's side rear corner of the tank. The vent line connection next to it, and the vent line connection at the front passenger side corner, both have restriction orifices in the nozzles.

The fuel vapour return line connection does NOT have a restriction orifice.
Thanks for the answer. I had it on my list of things to find out where it connects as I found mine broke the other day. It is not connected on the carb end so I will just plug it though.



Sent from my iPhone using Tapatalk
 
1 - 11 of 11 Posts
Top