Hi please can someone help me out. I have an early A12 motor (dizzy at the front of the block) I fitted a later A12 fuel pump to it and it won't work. I then put what I thought was the original pump back on it but it knocks and actually moves against the block !!!!!!!!!! I have had the engine for awhile sitting in my shed and it was working finne when i took it out of the car first can I fit a later pump to it and secondly why is the original pump moving against the block and has a distinct knocking comming from it I must have fitted it wrong some how. I am sure reading somewhere that pumps have a different lenght in the actuating arm. Would an A10 pump bolt up OK ?? I am buggered here.

Make sure you have fitted the spacer block between the pump and the block, and that the arm is on the right side of the cam.

I would bypass it and put a plate on the pump access to the block and buy an electric pump and reg and put that inline. The datsun pumps are reliable too if you can get a good 2nd hand one. But the electric pump will prime your car before you crank making fuelling much easier and starting easier. It will also be fairly silent in normal operation letting you know you have fuel being pumped...just a nice audible indication.

There is nothing wrong with the stock mechanical pumps as used on A series engines, but as you already know, you need the right one.
Fuel pumps for the A10 & 1200 engines interchange with each other. [Front distributor]
Fuel pumps for all of the 1974 & later engines [A12, A12A, A13ls, A13ss, A14, & A15] will interchange with each other, but not with the earlier engines [back distributor]

If I am installing a rebuilt or long stored engine, I prime the carb by removing the plugs & cranking it over till the carb is full. A side benefit is that it primes the oil system too.

i with dodge n this one, prime it first, wont give you any probs then.... but good to see al late model ones are the same... i always though a14 and a15 had a slightly longer arm on the fuel pump.

Thanks to all for your advice i took the pump off and checked it out and found the spring on the arm was missing and still is !!!!!!!!!!!!!!!! pit on a a10 pump and seems to be going gr8 now but the spring hmmmm hope it follows gravity and sits in the sump :)) once again thanks for your help