Why block the fuel return?

[DrWin]

So, I got the new fuel pump installed in the tank today (thanks to everyone who gave advice!)

Preparing to put the tank back in, I changed the softlines immediately before the fuel pump, and discovered this: :8ball:
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The connection between the hard and the soft line was closed with some hard wax/shrink tubing/whatnot. Under the white hard substance there seems to be plumbers tape wrapped around the place where the connector/adaptor meets the hard line.

As far as I can tell the return line has been blocked. Why would you do that, and what should I expect going forward after removing the blockage?

[Helirich]

Doesn't make much sense. Does your car have a carburetor? That's the only way I could see that working, but you would need a differnt pump. Was your car running before?

[Patrick C]

Doesn't make much sense. Does your car have a carburetor? That's the only way I could see that working, but you would need a differnt pump. Was your car running before?

I was going to ask the same thing...might make sense if it was carb’ed at one point.

[DrWin]

Thanks for the replies, guys.

No carburetor that I know of - it has a K-jet system on board that was newly restored when I got the car.

The car ran (poorly). At low speeds it would choke when braking and sometimes just on its own. It would sometimes have to give it a little gas AND apply the brake to keep the engine turning over when at a red light. Which I suppose makes sense if the engine couldn't return unneeded gas to the tank.

It would go into the chambers instead, causing a very rich mixture?

[Ron]

Thanks for the replies, guys.

No carburetor that I know of - it has a K-jet system on board that was newly restored when I got the car.

The car ran (poorly). At low speeds it would choke when braking and sometimes just on its own. It would sometimes have to give it a little gas AND apply the brake to keep the engine turning over when at a red light. Which I suppose makes sense if the engine couldn't return unneeded gas to the tank.

It would go into the chambers instead, causing a very rich mixture?
No, the pressure in the lower chambers is always PP.
The upper chambers are always 0.1 Bar below PP. (So they and the differential valves there have nothing to do with Air-Fuel ratio...the plunger handles that alone.)
The mixture would go lean because the CP would raise to the PP, just like a clogged WUR/CPR outlet....or when you shut the gauge valve.

COLD = Lower CP = Larger Plate Gap = Higher Plunger = Larger Plunger Gap = Richer
WARM = Higher CP = Smaller Plate Gap = Lower Plunger = Smaller Plunger Gap = Leaner
[If this seems wrong- Note the ISM will keep the RPM constant, so the air intake will remain constant.]

[Rich]

So, I got the new fuel pump installed in the tank today (thanks to everyone who gave advice!)

The connection between the hard and the soft line was closed with some hard wax/shrink tubing/whatnot. Under the white hard substance there seems to be plumbers tape wrapped around the place where the connector/adaptor meets the hard line.

As far as I can tell the return line has been blocked. ......

There is another possible explanation to what you found.

Perhaps a previous owner somehow replaced a segment of the original (damaged?) return line and with a different return line between the engine and the fuel tank. And perhaps part of that return line is now located somewhere you haven't yet looked?

I don't know why someone would do this - it is only an unlikely theory for now.

[David T]

If the fuel system is still "stock" the best advice would be to try to return the fuel system to as stock a configuration as possible. Start at the PPR and see if there is a return line there and how it is (or isn't) connected. Work your way back to the tank and get the return line to work. Check what was done in the area of the fuel accumulator, one line from it tees into the return line.

[82DMC12]

There is another possible explanation to what you found.

Perhaps a previous owner somehow replaced a segment of the original (damaged?) return line and with a different return line between the engine and the fuel tank. And perhaps part of that return line is now located somewhere you haven't yet looked?

I don't know why someone would do this - it is only an unlikely theory for now.

This is the most logical answer. They probably couldn't get the fuel line to come apart at the compression fitting, mangled it, and was forced to run a new line somewhere else. They then cut out the bad area and did a really interesting job of sealing it off. There's no way it's connected to the engine, either. Fuel pressure would eventually blow the plug out.

[DrWin]

That's what I'm trying to do. I have no intention of heavily modifying the car, my mission is first and foremost to get it working again. :D

As it turned out, the blocked fuel line WAS connected to the engine and as soon as I started up the engine fuel came out of the return line. It was orange and smelled horrible, but I think it was once fuel. Got the first couple of litres into a separate tank before hooking the return line up to the car.

Car runs better now. Less noise, less soot, no tendency to choke at deceleration.


If the fuel system is still "stock" the best advice would be to try to return the fuel system to as stock a configuration as possible. Start at the PPR and see if there is a return line there and how it is (or isn't) connected. Work your way back to the tank and get the return line to work. Check what was done in the area of the fuel accumulator, one line from it tees into the return line.

[Ron]

That should of shown up in the control pressure readings (too high)...Do you have a gauge set? If so, I'd check them. And then the CO.