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MG MGB Technical - Fuel pump not working

After a complete "original" renovation of a 1963 MGB (originally from Texas) it is finally time for starting up. Installed two 6 V batteries today and filled 10 l of fuel in the cleaned tank.

When I turnend the key I could hear the fuel pump working. But no fuel came to the carburettors. Why? Can the pump run "backwards? Can there be an air lock at the suction side?

The pump I have installed is a new SU from Moss with number AZX1332 (positive earth). The white wire from the new wiring harness is connected to the small end of the pump and the black ground wire to the pump housing. When I look at the electrical wiring diagram it looks like that is correct. But is it?

The instruction following the pump says that the pump is "polarity conscious" and that the pump will be damaged if connected the wrong way, and not work. Because of that I hesitate to change the wires even for a test.

Can anyone please come up with a proposal what to do.

Goran Svensson

I know it sounds silly but you have the pipes on the right sides as it a pull from the tank and push to the carbs
Ste Brown

Goran - To reinforce what Ste Brown stated, make sure that the pump is installed properly and the fuel line from the tank to the pump is going to the inlet fitting and the line from the pump to the carburetor is going to the outlet fitting. This may sound obvious, but I have answered several queries where the pump was hooked up incorrectly. With the pump mounted such that the two threaded holes in the alloy pump body are aligned horizontally, the outlet fitting should point straight up and (viewed from the back of the pump body) the inlet fitting is at about 2 o'clock. If those connections are reversed, the pump will not pull fuel from the tank and push it to the carburetors. If the connections are correct, then you probably have an air leak on the inlet side of the pump. An air leak can occur at any junction of the solid line and a flexible line, at the connection to the pump or to the tank fitting or the pickup tube could have a hole in it above the level of the fuel in the tank and finally (and most embarrassing cause) not enough fuel in the tank. Cheers - Dave
David DuBois

Source of problem could be also air. Remove the pump from the bracket and put it on the floor, disconnect inlet hose and suck out air (I used my mouth but I do not advise you to repeat that, use some transparent extension hose so you can see when is fuel coming out). Reattached inlet hose to the pump and let it run when is laying on the floor as long as you do not get fuel to the carbs and then install it back to car. That solved my problem so maybe can help also in your case.
Toni Kavcic

Hi again,
And thanks for your comments. After checking the installation and finding everything ok I checked the suction line as Toni proposed. Connected an external pump to see if this one could suck fuel. Same result, nothing came out.

After that I made a "blow" through the tank outlet with compressed air and then something blow away before bubbles came in the fuel. After that the original pump worked without problem. Probably I had got something in the tank outlet pipe when I cleaned and sealed the tank inside.

With fuel in the carburettors I turend the key for start and the engine started directly! After a total 6 year renovation of of the car, including the engine.

Soon time for swedish registration and after that many lovely trips I hope.

Goran Svensson

Did the engine get a re-build? then for sure run it at least 20 minutes with say 2000 rpm to bed in cam surfaces rings etc. Then drain the oil and check for bits, new oil then, can ( be the very best.) Cheaper oil for the bed in, ( not too cheap! ) Mike
J.M. Doust

"Probably I had got something in the tank outlet pipe when I cleaned and sealed the tank inside. "

Very common, can be terminal! let's hope it isn't a lump that's going to get sucked up to the bottom of the pipe and block it again. Originally the bottom of the pipe had a strainer, which is why blockages occur, and you may have blown this off. You may also have blown out a weak section of the pipe, which will give you a low usable fuel capacity (It's being so cheerful that keeps me going ...)
PaulH Solihull

This thread was discussed between 20/06/2011 and 22/06/2011

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