260z Mechanical Pump

W

Weldmast

New Forum User
I am restoring a 260z which had stood for several years and have been trying to start the engine. The mechanical fuel pump was full of a tar-like substance, presumably old petrol which I cleaned out, but couldn't get the pump to prime, on the car although it did do reasonably well on the bench.. I obtained a used pump which works perfectly sucking fuel from a container whilst on the bench. When fitted to the car this pump will also not prime, even from the same container. It would appear the lever arm on the pump is not being actuated enough to draw up the fuel. Can anyone help with this? Does the lever arm drive straight off a cam lobe, or is there a cam follower which may be worn/missing? The pump is bolted to the engine and has a spacer approx 6mm thick between it and the block. I am baffled. Be glad of your input.
 
Hi, there is an eccentric drive for the pump which should be fitted between the cam sprocket and its mounting bolt, just lift the cam cover and take a look !
 
if the eccentric on the cam is holding the pump arm up it will not prime as the diaphragm can't move. fit the pump and inlet pipe with outlet pipe into container and check for fuel.
 
Just make sure that the Pump arm is actually engaging onto the lobe of the eccentric - remove the Rocker Box & check - easy to miss it when fitting a new pump into the aperture.
 
Thanks for all your help guys. The lever is engaging on the eccentric but it doesn't move the lever enough to pump. I have tried stretching the diaphragm spring but still no go. Again when off the bench, and the arm is moved manually the pump work fine. Could it be that the diaphragm is weak?
 
This may have absolutely nothing to do with it but do you jave the plastic packing insulator installed between the pump and the head?
 
There is an insulator/packer between the pump and head, approx 6mm thick. Both the original pump, and the secondhand pump I obtained have the same size spacer. If anything the pump body needs to be nearer the head. I assume the spacer is to prevent fuel foaming through vibration or similar?
Another question, how much free play should the lever arm have? Mine appears to have at least 25mm of arm movement before pump will start to prime.
 
Bite the Bullet and buy a new one - they don't last forever !
And yes, you do need the spacer in place to get the correct result - it was designed to be there, so leave it there....
 
Weldmast said:
Thanks for all your help guys. The lever is engaging on the eccentric but it doesn't move the lever enough to pump. I have tried stretching the diaphragm spring but still no go. Again when off the bench, and the arm is moved manually the pump work fine. Could it be that the diaphragm is weak?
Click to expand...

Could be the diaphragm - if you want to try the pump from the other engine (260z) I've got you'd be most welcome :D
 
I had trouble priming the fuel pump on my 260Z after a long lay up and created a cheat method. I took apart a cheap bicycle pump and turned the valve around then pinned it in place. The bike pump now sucks rather than blows.

Suction at the fuel line of one carb while blocking the fuel line at the other and I soon had the fuel where it needed to be.
 
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