Are the twin tanks in the Mini interconnected meaning you can fill up on either side and the pump will pull fuel from both?

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1973 Clubman GT - YG2S8 1637

yes the same as a Cooper S.....but remember the interconnecting pipe is only about 1/4 or 5/16 diameter so it will take quite some time for the fuel levels to balance up.....if you only fill one side, the other side will be mostly left empty until the levels balance up

I filled one side 3 gallons (right side) and the other side about 5 (left side) after my car stopped and ran out of gas.

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1973 Clubman GT - YG2S8 1637

There might be a blockage in the tube joining the 2 tanks.
If the fuel gauge shows you are nearly empty, fill RH tank only (about 1 to 3 gallons should work). Go for a short run and the fuel gauge should slowly rise. This shows the fuel is moving from the RH tank to the LH tank, which has the fuel gauge unit in it.
If the car runs out of petrol again, even with petrol in the RH tank, you have a blockage stopping petrol getting from the RH tank to the LH tank and the petrol pump under the floor.

You can also have a block in one of the tank breather pipes, which will cause one to stay higher than the other tank

I added a RH tank and during one drive the RH tank breather got blocked, and caused it to stay full while the other tank was nearly empty

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Is the connecting pipe under the boot floor?

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1973 Clubman GT - YG2S8 1637

Above floor. Steel pipe.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The interconnecting tube is running between the 2 tanks at the bottom of the rear seat vertical panel. The long braided hose that disappears through the floor near the LH tank goes down to the fuel pump. Fuel can move from tank to tank (if the car is parked at an angle), and both tanks can feed the fuel pump under the boot floor.

There is no switch to select which tank is used by the pump.

Strange that 1 tank has more fuel than the other and it would not run with the LH tank empty

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1973 Clubman GT - YG2S8 1637

That is why it suggests a blockage somewhere that is stopping fuel getting out of the RH tank.

If you filled the LH tank only but nothing in the RH tank, does the fuel level in each tank equalise after 5-10 minutes?

Sounds like you are getting closer to having to drain the tanks and have a good look at the lines, hoses and connections, checking for blockages.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

There is a small nylon strainer on the outlet pipes in both tanks - one of those could be the problem.

It’s also possible that the PO has incorrectly fitted one of the rubber hoses on the end of the steel joining pipe and it’s kinked underneath the tank. Mine had one length that was too long and it was folded in on itself to get it in there
Neil

One of these was blocked on mine after I rust converted the tank.
I put a drill through it and fitted a filter before the pump.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I got to find the time to do this, thanks everyone

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1973 Clubman GT - YG2S8 1637