Fuel pressure issues....

[RichOakley]

Has anybody ever experienced fuel pressure issues with their 25hp fuel pump and 26VFI/VFIS carb??

My '47 has always suffered fuel probelms ever since I bought it. I used to be able to drive it a few times and then it wouldn't re-start. The plugs would get so black and sooty, it would prevent them from sparking. At first I suspected the 26VFIS carb, so I rebuit this and set it up correctly. This made no difference. So I fitted a NOS 26VFIS carb. Same problem. Just to make sure I wasn't going mad, I then fitted a rebuilt (and correct) Huf 26VFI carb. Same problem occurs.

My attention then turned to the fuel pump. I took this apart and rebuilt it with a new rebuild kit. I made sure the pushrod travel was within specified limits (it was bang in the centre of the specified tolerance). Fitted everything back together and still suffered the same problem.

I handed the car over to Ian Clark at Wolfsburg Performance Services to be looked-at. Ian also did a lot of head-scratching and then decided to construct a fuel-pressure gauge set-up in the 8mm line between the pump and carb. To Ian's surprise, the pressure was running at 6psi (it should be 1.5psi). It was concluded that shimming out the pump pedestal with an extra gasket should solve the problem, so this is what he did. Adding a 1.5mm-2mm gasket should have made relatively little difference to the fuel pressure, but it reduced it to zero!! So a day was spent crafting ever-thinner gaskets, re-fitting the pump, to get the pressure just right. He eventually got it running at around 1.5-2psi which solved all the problems. The car ran without any problems whatso ever after that. Then a 'rod snapped in the bottom end and a rebuild was on the cards.

After the re-build I am now back to square one with massive over-fueling. Has anybody ever experienced a massively-over sensitive fuel pump problem like this before?? I would be most grateful of any suggestions!!

Thanks,
Rich.

[Peter_Plade]

Sounds strange.
If the push rod travel is correct everything should be fine.
I use the original tool to measure the travel but I'm sure you have that too.
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[RichOakley]

Thanks Peter.

Yes, the pushrod travel is correct. Going to try and compress the diaphragm spring and see if that makes much difference. Also making up a fuel pressure gauge so I can measure it accurately.

[RichOakley]

Ok, problem solved (I hope)!!

After figuring that everything else was correctly set, I pulled the fuel pump apart. I rebuilt this a while ago and it made no difference at all.

The original workshop manual suggests that if the pushrod is set to the right length of travel, you should reduce the size of the diaphragm spring in the pump. I checked a few aftermarket rebuild kits and they all have the same standard size spring. So, I took my spring and after a lot of gentle tweaking, managed to decrease its overall length by 10mm.

I fitted everything back together and made an in-line pressure gauge. The fuel pressure is now perfect at around 1.5psi...

I hope this has solved my fuel pressure woes, but I won't be able to find out until I get some new ferrules delivered to re-fit the fuel line.