SU Fuel Pump Points Adjust

Background: Fuel pump quit (not clicking). Tapping with hammer did nothing. Removed the pump and installed the transistor mod. I cleaned the points and it would only pump a couple of beats. See the attached picture. There is a point adjusting screw in the middle of the points. I depressed the hex nut holder and tightened the screw (making the point gap narrower). The pump is now clicking as it should but still not pumping fuel. Apparently there are several iterations of these pumps. Does anyone know what the point gap should be set to?

Various stuff I have all suggests about 0.030". This is from the manual

Eric
Shropshire, UK

Burlen also has instructions that might be helpful

http://sucarb.co.uk/technical-electrical-fuel-pumps-reassembly

Thanks for everyone’s help but my saga continues. My pump is now “clicking” as it should. I installed it in the car but it would not pump from the tank. I connected a separate gas line to the pump’s inlet and filled it with gas and it pumped the fuel correctly. I understand that the gas tank fuel pick up line runs from the bottom of the tank and exits at the top. It is like my pump does not have enough suction to pull gas from the tank when the line is not full of gas. When it is full of gas it will siphon keeping the pump primed. My concern is that if I run the car out of gas, the pump would not be able to pull fuel from the tank once the feed line is empty. Do I have something set incorrectly? The pump diaphragm does move up and down but perhaps it has stiffened with age? Do any of you know where I may be able to send the pump for repair if necessary.

I would check the valves in the pump.

Not sure how this ending up on the engine forum, but anyway, the SU LCS pump should be able to suck up about a liter or a quart per minute from 33 inches below, and push it up 48 inches above.
This information comes from the Mark V Service Manual page B40.
Your disc valves could be stuck as Robin suggests, but I think it more likely that the diaphragm is old and stiff. I had to replace the one in my 120 last spring because it was about 25 years old and wouldn’t pump anymore. New diaphragm from Moss Motors and it has been fine all summer. They are very easy to replace. For the square body pump you want the long stem version. The short stem version is for the round body pumps found on MGs.

Thanks. I think you are right. Recently my HD6’s started leaking gas and it turned out to be the rubber jet diaphragms - hard and brittle. I wonder if the ethanol in the gas caused not only that but the fuel pump diaphragm as well. Do I have to take the pump points mechanism out to replace the diaphragm?

Pat H

No, you just screw in the stem. The tricky parts are two: The threaded bit in the points tends to spin around making it hard to get the stem thread started. And you don’t screw it in all the way, just enough so the points throw over properly. Push it with your thumb and watch the points operate.
There are 11 little brass discs that have to fit in there. Then put some fuel proof sealant on the contacting face (not the brass disc side) and screw the 6 screws down evenly.

Thanks again! SNG doesn’t sell the part. I called XK’S Unlimited (usual disclaimers) and the have them for around $40 or so BUT they also sell a rebuilt like new, transistorized unit for around $180. Sold!

Taking all this into another topic…Could all my woes (brittle jet diaphragms, pump diaphragm) be due to ethanol laced gasoline? I wonder if the new replacement parts are made of materials ethanol tolerant. Maybe this is just an issue for us US folks but certainly something to be aware of.

Pat H

My Mark V has been using ethanol blend gasoline in California since it was introduced there. I’m thinking it was at 5.7% for years and then about 2010 California switched to 10% ethanol. I’ve never noticed any negative effects due to ethanol in the more than 15 years I’ve owned the car. Whatever comes out of the gas pump at lowest octane available works fine in my car driven about 1,000-2,000 miles per year.