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Venting fuel tank dilemma

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jseabolt Avatar
jseabolt James Seabolt
Mount Carmel, TN, USA   USA
1977 MG MGB
My 77 has been desmogged. The only thing left was the vapor separator in the trunk which someone took me up on my offer to give it to them. The charcoal canister has been removed in the engine compartment. But the 1/4" line is still there.

When I opened the trunk yesterday, I got hit in the face full of gas vapors venting off the separator. And it's not even summer. Yet the separator was connected to the metal line, there was a hose that was venting inside the trunk which a bunch of zip ties.

I just ran a hose from the filler neck to the metal line. So now vapors will be venting into the engine compartment. Still not a very good idea. However I had a reason for this I'll explain below.

One idea was to look for a vented fuel cap from an older MGB. But typically a vented fuel cap won't screw onto a filler neck if the car has a vapor recovery system. Just for that simple fact so people don't use a vented fuel cap.

So I am probably answering my own question. Will a non vented cap fit a 77 model? Or do I need to source an older filler neck?

I could connect a hose to this nipple and knock out one of the clear plastic plugs, replace it with a grommet and run the hose to the ground. I have done that before.

The main reason I'm asking this is there is no fuel return line coming off my Weber carb. Someone has installed a high volume Facet rotary vane pump. I have not tested the deadhead pressure of the pump but I do know that Weber's don't like more than 3 PSI and I bet it's more than 3 PSI. This could cause the engine to run rich if it does not blow the float valve off it's seat. I've had that happen before!

Even cars with Webers and mechanical fuel pumps have a 1/4" return line. Do you see where this is going?

If the pressure is more than 3 PSI, I got a few options. Install a regulator between the pump and carb. I do have a regulator.

The other idea is to install a 5/16" X 1/4" X 5/16" tee before the carb and use the 1/4" vapor line as the return line and just dump excess fuel back into the tank through the filler neck.

But I still need some way to vent the fuel tank. One idea could be to modify the cap. Like drilling a small hole somewhere . Or remove the gasket. I don't know if removing the gasket would be good enough.

Anybody ever dealt with this same dilemma?



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1977 MGB
1980 Fiat 124 Spider (turbo)
1987 Yugo (1500 turbo)
1981 Trabant 601
1987 Citroen 2CV
1968 Ford Fairlane 500

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lewk Avatar
lewk Silver Member Keith Lewis
Cambridge, ON, Canada   CAN
Drill a hole in the gas cap, best solution for now. Best solution overall is to take it back to original with vapour separator and charcoal canister.

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riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
I answered in your other thread but ..............

If you were to re install the balance of this evaporative loss system you would only be able to recapture the fuel tank vapors. Your downdraught carburetor float chamber vents to atmosphere.

Simply cap the fuel tank vent in the boot and drill a vent hole in your existing fuel cap. Many owners do this it works.

B



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PatrickLewis.net Avatar
PatrickLewis.net Patrick Lewis
Brandon, FL, USA   USA
1974 MG MGB GT "Green Monster"
1977 MG MGB
I have done the hole in the cap, but it did not quite work for me. I kept getting a vacuum in the tank.

I bought a vacuum relief valve and installed it in the rubber hose filler neck. I added two stainless steel flat washers (bent to match hose curvature) to hold it tight to the filler neck.

This is what I bought:

Adjustable vacuum relief valve





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ex-tyke Avatar
ex-tyke Graham Creswick
Chatham, ON, Canada   CAN
1976 MG MGB
Quote: I have done the hole in the cap, but it did not quite work for me
Then, I assume that it wasn't done correctly!......just requires a 1/8" drill through the metal disc.


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PatrickLewis.net Avatar
PatrickLewis.net Patrick Lewis
Brandon, FL, USA   USA
1974 MG MGB GT "Green Monster"
1977 MG MGB
I did a 1/16" hole just like that, but I think there was something behind the metal that rotated and closed the hole.



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ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
Dump the fuel pump, don't use a regulator, unless it's one that cost more than a pump. The cheaper ones don't work for long. Get a proper SU, Hardi or Ecco, with psi ratings around the 3 psi value.

Block off or remove all extraneous plumbing and drill a hole in the gas cap, do a search for how and where.

Herb



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lewk Avatar
lewk Silver Member Keith Lewis
Cambridge, ON, Canada   CAN
Here's the fuel pump I use and it works great, no regulator required, available on eBay.


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Steven 67GT Avatar
Steven 67GT Steven Rechter
Jackson, CA, USA   USA
Get a fuel tank filler neck from an earlier model. You will have a better selection in quality vented fuel caps with the earlier style mounting tabs.

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jseabolt Avatar
jseabolt James Seabolt
Mount Carmel, TN, USA   USA
1977 MG MGB
So basically just drill a hole in the plunger, not all the way through the cap itself.



http://s222.photobucket.com/user/turbofiat/library/?sort=2&page=0

1977 MGB
1980 Fiat 124 Spider (turbo)
1987 Yugo (1500 turbo)
1981 Trabant 601
1987 Citroen 2CV
1968 Ford Fairlane 500



Edited 1 time(s). Last edit at 2019-03-13 05:32 PM by jseabolt.

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MCARD Avatar
MCARD Mathew Mathew C Card
Warren, RI, USA   USA
1980 MG MGB
Hi James, yes drill the 1/8th hold in the plunger like the photo in Graham's post above. I have done this as well and it has worked out well with no issues. Good luck!

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hotrodmg Avatar
hotrodmg Alan L
Arlington, TX, USA   USA
You will be drilling through 2 or maybe 3 pieces of metal sandwiched together with the rubber gasket. On mine it wasn't just one metal layer I drilled through, I also clipped the head of the rivet that holds the gasket plate together. I should have drilled my hole a bit further out from center.

I ran a paperclip through the drilled hole to check that it touched the inside of the domed cap skin.

The goal is to drill through the entire gasket plate assembly to open up into the spring/domed cap inner area that is open to atmosphere, not through the outer domed cap skin.

In reply to # 3908237 by jseabolt So basically just drill a hole in the plunger, not all the way through the cap itself.

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