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MG MGB Technical - Fuel Tank filling problem

When I fill my new fuel tank,in my 79 B it only fills to about half full then to fill the last 20 liters I have to trickle the fuel in. I have checked the vapour system and it appears clear. The tin can is empty & I can blow thru it.
I tried disconnecting the fuel vapour connection at the cannister but it makes no difference in the fuel filling rate.
The problem reminds me of a marine diesel fuel tank I once had where the filler pipe extended well down into the tank.
My impression is that air is not escaping from the tank.
Final point, it is hard to suck or blow thru the fuel vent line to the cannister.
This problem became apparent in our 2900 km trip thru the interior of BC and I was unwilling to risk fuel in the trunk while travelling.
Oh,our fuel now contains 10% ethanol.
All help appreciated as it is a real pain to have to kneel on the ground peering into the fuel filler & trying to fill the tank without pouring fuel on the ground.
All help greatly appreciated.
Thanks
Morris
M E WADDS

With such a small breather pipe from the tank through the separation chamber to the charcoal filter, and the resistance of that, I can't believe the displaced air from the tank during filling can only escape that way, if the nozzle seals to the filler to prevent fumes escaping to atmosphere isn't there a suction system as part of the nozzle? In any case my understanding is that the pump nozzles shut off when they draw droplets of fuel back through a little orifice at the end of the nozzle, i.e you are getting splash-back not a restricted breather. If the breather were restricted or blocked you would get running problems from fuel starvation as the tank developed a partial vacuum and overcame the pump.

Is this with multiple filling stations? Some are more sensitive than others. Some will only deliver full flow if the nozzle is angled in the filler neck either up or down, some won't deliver full flow at all so I have to not pull the trigger all the way, some have to be partially withdrawn to deliver full flow. Others deliver full flow at any angle and fully inserted.
Paul Hunt 2010

Thanks Paul. I am in the process of replacing the charcoal in the cannister. I thought maybe there was a restriction in it but there wasn't. I was suspicious when it was hard to blow back from the trunk to the cannister
I pulled the rubber filler hose from the tank to see if there was a restriction in either the filler pipe attached to the car or in the tank and nothing. But, I realized the metal filler pipe welded to the tank extends a full two inches into the tank. Much less but similar to the old marine diesel tank. I now think that the extended filler pipe is the source of my problem.
I calculated the volume of the tank above the filler neck to be about 14 liters which is close to the volume of fuel that I had to trickle into the tank to fill it.
This is not a big problem around town to be able to fill the tank only 3/4s but there are many places in BC where the gas stations are few and far between and one wants a full tank when starting out and having a good idea how much fuel there is and the mileage.
To answer some of your questions.
We refueled about 7 times all at different stations.
The fuel pump nozzles worked normally & shut off when the fuel rose in the filler neck.
I don't push the nozzle in too far so that the rubber shield closes off the escape of fumes & I fueled the same way with the old tank.
Once this happened I had to get on my knees with a small flash light and feather the fuel delivery with the nozzle pulled way back and just inside the filler tube so it wouldn't shut off. Using this method I was adding from 11 to 20 more liters of fuel.
I would greatly appreciate it if someone with an old tank would measure how far the fuel tank filler pipe extends below the inside top of the tank. I suspect the new MGB replacement tanks are not built the same as the original.
Thanks
Morris
M E WADDS

When I fill up my B I have to manually move the rubber collar, on the filler line, rearward to get the fuel to flow. If I don't, the fuel will stop flowing. I have to pull the hose from the pump as far as it will come and actually stand on it while I fill up my tank. This requires my having to bend over at a very uncomfortable angle. This little ceremony has become a royal pain just to keep some fumes from escaping in to the atmosphere. RAY
rjm RAY

Ah, in NZ we don't have any of that escaping fumes malarachy on the petrol pump nozzles. We're a clean, green, petrol fume smelling country!

On mine I had welded some perforated steel to the filler pipe to stop siphoning but that just caused fuel to gush out the back when filling unless you only partly pulled the nozzle trigger to really slow the flow.

I removed that and it works much better now but I still find you have to be careful and you will get fuel splashing back if you leave it on full. Like Ray this means I am having to stand, bent over, hand on the trigger making sure it fills up OK.

The filler extending into the tank is odd. I have two old tanks and the one in the car and I am pretty certain they are all flush with the top and don't extend into the tank at all but need to confirm (involves going under the house with the spiders to check so maybe this weekend).

Simon
Simon Jansen

Morris, it may be that your "new" fuel tank has a manufacturing defect in that the fill tube is set too far into the tank.

I have no problem filling my GT unless I have the gun on full force as it gets near full - about 2 litres to go.

Can you compare with the old tank? Refund/replace?

John
J Tait

Had a look at the two rusty tanks under my house. One has a short filler and the other a slightly longer, bent one but neither have the filler pipe extending into the actual tank itself.
Simon Jansen

That extension doesn't seem right, and it would mean that the only way you could fill above that level is to do it slow enough for air to vent via the charcoal canister, which even if the vent pipe is disconnected from the tank is only a very small diameter, it's acting like a second capacity reduction device. The tank should already have an open-bottomed cylinder with a bleed hole at the top which reduces capacity by ten litres, this seems to be reducing it by another 20 (unless you are very patient)! If you choose not to replace maybe you could cut or drill into the extension a large enough hole or slot to allow air back out into the filler neck at a decent fuel flow rate.
Paul Hunt 2010

Thanks to all who have responded. I was able to locate three original MGB fuel tanks. The filler pipe protruded into the tank from 1/8th to 1/4 of an inch.
The total length of the original filler pipe is 2 inches.
In my replacement tank the filler pipe is a full three inches long and appears to extend into the tank about 2 inches, maybe less as it is hard to determine how much of the filler pipe lies above the tank as it is of course installed.
For the last three fill ups I was able to trickle in about 14 to 15 liters of fuel after the nozzle shut off
I did a calculation of the volume of fuel contained in two inches of the top of the tank which is about 14 liters.
This tank was made in Quebec Canada.
The only way to make this tank fill properly is to pull it and cut in a 1/4 inch slit full length of the filler pipe inside the tank. I am not going to do this but I am going to request a replacement fuel tank which is constructed correctly.
I understand there are other suppliers.
I would suggest that if you purchase a new tank to be sure to check how far the filler pipe protrudes into the tank because any volume above the bottom of the filler pipe is wasted.
Thanks again
Morris
M E WADDS

I put the filler nozzle into the tank upside down. You don't have to bend double to hold it, and it seems to fill much faster without cutting out all the time.

David
D Balkwill

Like David I'll sometimes put the nozzle in upside down. This does seem to help.

However I think you found the root of your problem with that 2" extension into the tank.

As a temporary solution you might be able to take a curly piece of plastic tubing (like on a coilded air hose) and stick it into the tank so it curls back up above the bottom of the inlet when filling.

BH
BH Davis

Thank you BH, I will give your suggestion a try. I just filled the tank so it will be a while before I can report back.
Cheers
Morris
M Wadds

This thread was discussed between 12/06/2010 and 17/06/2010

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