AC fuel pump advice

[Paul Singleton]

Although I haven’t seen it, apparently the push rod wears and then there isn’t enough stroke to operate the fuel pump. Old timers apparently would add braze to the top of the rod to restore the length lost to wear.

[Ron Pier]

That's another option Paul, although I don't seem to be getting full stroke when working the operating arm by hand. Anyone know what length the push rod should be and what's involved to remove it?

Thanks Ron

[Richard Farrant]

Hi Ron,
I have rebuilt countless AC pumps over the years and always check for suction and pressure with a thumb over the ports. Doing this before fitting to the engine. Sometimes it needs a bit of petrol squirted into the pump to wet the valves before it will suck of pump then they are OK. There is often a bit of free play in the lever before the take up the stroke. As someone suggests it could be the push rod is worn.

regards, Richard

[Ron Pier]

Thanks Richard. I haven't reamed through my manuals to see if there is a push rod length given or how it comes out. It's just that if I act as the push rod with my hands, there doesn't seem to be much downward movement of the diaphragm when I'm at the top of the stroke???

I haven't run the engine for a few months but it's never been a problem, so I assumed the diaphragm had dried out or cracked?

Cheers Ron

[Andrew Rowe]

Do exactly what Richard says after assembly , and this will confirm operation of pump. Just remember, when you reassemble, compress the diaphragm by holding the lever up BEFORE you tighten the top screws up. By checking the pump action will also indicate that you have the valves around the right way as well as diaphragm action. Other than that the problem will lead you to the length of the push rod. You can sit the pump on the engine , but do not bolt down, turn engine over to observe the lift of the rod and the effect this is having on the pump, it should push the pump up and down when not bolted to the manifold, also check the condition of the gasket under the lid,to seal and also any holes in the main diaphragm, as this will also lead to faulty operation, Cheers Andrew.

[Richard Farrant]

Originally Posted by Ron Pier

Thanks Richard. I haven't reamed through my manuals to see if there is a push rod length given or how it comes out. It's just that if I act as the push rod with my hands, there doesn't seem to be much downward movement of the diaphragm when I'm at the top of the stroke???

I haven't run the engine for a few months but it's never been a problem, so I assumed the diaphragm had dried out or cracked?

Cheers Ron

Hi Ron,
Something else, make sure the sealing ring for the sediment bowl is in good order too.

Richard

[Lynn Eades]

Amongst us, most things have been covered. but here are a couple of other hints:
As Richard said, make sure the sight bowl seals properly or you will never get it working like it should. Sometimes the alloy is distorted.
Replace the seal around the diaphragm rod. It stops you sump filling with petrol if your diaphragm leaks. Make sure the drain hole to the outside is clear.
Some times the wear occurs at the pivot and you get lost motion. (your last picture, this is where part of the pump stays still while the other part is still moving)
What Andrew says is very important about tightening the screws. It restricts the delivery vol. (the spring dictates delivery pressure) The diaphragm must have enough material inside the pump to move freely, so activate the pump to its maximum travel and tighten the screws in this position.
I hope that helps.

[Ron Pier]

I'll have another play with the pump today. with everyone's tips and hints in mind. I have worked on these mechanical pumps before. I was a motor mechanic in the 60's and 70's when they were quite a usual fitment.

When I fit the glass bowl, I can blow and not suck to prove that the one way receiving valve is working and that the bowl in not leaking. Likewise I can suck and not blow at the delivery valve end. There's something I haven't worked out about the travel of the diaphragm......On the bench.

Cheers Ron