Rebuild fuel pump points verses convert to the electronic points as per the form

I’ve been having a discussion with Dennis regarding fuel pump rebuilds
what’s the group think of old school points verses installing the transistors to off load the points after installing new points of course there’s a post regarding this mod
Let it fly
Ian Wrote: “The most unreliable part of the SU pump is the Points
system. If you do
like me and rebuild the pump, new diaphragms, valves and points and at
the
same time install the Transistor mod, the pump will run for years. I
did
mine about 10 years ago and it still runs perfectly. More
importantly, it
still provides tha Click, Click, Click sounds that we all want to
hear.”==================
Cheers jim

I used to think it was far better to replace the old SU pumps with an electronic equivelant but after so many newer failed pumps my opinion has changed.
I would trust an old SU pump for my daily driver because I know I can alway get it working again-even if I got to tap on it a few times.

2 Likes

As you say, a tap is usually all it needs.

When I bought my V8-250 I believe the fuel pump was original (50 years old) but required the occasional tap. After getting an incorrect replacement pump from one supplier I 'phoned Burlen who knew exactly which pump I needed and it arrived 2 days later. Never had any problems since so I consider it £100 well spent - you soon forget how much it cost when your engine no longer cuts out !!!

I don’t know how it’s constructed but it goes ‘tick tick tick’ like everyone wants it to :smiley:

I took the old pump to a local Morris Minor expert who reconditioned it for me for £25 and said it would now be as good as new, so I have kept it as a spare. He should know, as he’s been doing it for 40 years or more.

So I think either way would produce a satisfactory result as long as your reconditioner knows what he’s doing, or you buy your new pump from someone who knows what they’re doing.

I rebuilt my pump with points 20 years ago when I got my car. Then a couple of years ago I thought to take it out and check it.

The points were heavily worn from arcing but the spring was not broken.

The rebuild kit had a varistor that reduces arcing so I rebuilt it and expect no problems until my kids take my license away and sell the car!

My view is that upgrades are well spent in other areas.

  1. For Jim and I (who had well over 30 degree C weather here in Vancouver last summer for the first time ever) it is a good idea to ensure car does not overheat. I have a series 2 cooling fan upgrade kit I am installing now. With adjustable fan turn on temperature. Twice the airflow using half the amps

  2. Some sort of electronic points. I put in a Pertronix

Dennis

1 Like

When I replaced my old SU pump, I bought a new one with points, instead of an electronic version, for that very reason.

f you have a new pump then there is little to be gained by making any changes, but if the pump is old and the points are semi life expired, then the transistor modification makes a lot of sense. This is because a transistor is a current multiplier, so only a fraction of the required current goes through the points.

See XK Tranistorized Fuel Pump for a discussion of the topic and SU fuel pump electronic upgrade for a solution which that requires no soldering.

You are welcome to do your own, but the very messy rat’s nest of components in some of the DIY examples featured n the above thread doesn’t inspire confidence in the result.

kind regards
Marek

1 Like

Learn a new fact-a-day!

The relevant part of the datasheet is the hfe number. For the TIP31 and TIP32 this is typically between 25 and 50. This means that a current of just 1/25th to 1/50th flowing through the points allows the full pump current to be switched by the transistor.

Put another way, a peak current of 3 Amps through the points becomes just 60mA. The points no longer arc and wear and tear on that account is frozen.

kind regards
Marek

2 Likes

The transistor doesn’t replace the points, it just offloads the current. Somewhere I saw a full electronic conversion that used an optical trigger to replace the points. Similar concept to the old Crane distributor kit. I don’t think it was here, maybe on an MG board.

I put this up on a recent thread - I have had this conversion for 30 years and it works well. Still uses the points as a switch and fits into standard housings.

Electronic Fuel Pump

1 Like

Rebuilt mine with the kit . so far works perfect But have not began trips ( snowed in till April ) I like I have factory matched with proper low fuel pressure adjusted to match carbs .

So far most seem to favour the old points and are In different to adding the transistor as they feel no practical improvement … Based on life expectancy The pump or them :laughing:
Jim

I think I know the answer to this but let me ask anyway.

I have the genuine replacement electronic version of the SU pump from Moss. It’ll be quite a while before any fuel is circulating in it’s veins so the question is, is it OK to run the pump dry for a short while to test it?

Obviously this doesn’t test pressure or flow but I haven’t heard the comforting tic tic tic in many many years and could use the encouragement.

Rick OBrien
65 FHC in FL

No: a short test will not damage it.

Will this conversion work for both positive and negative earth cars?

John
678462

There’s a post in the archives about it and apparently it will with some minor connection change . I also saw an old post in the archives about the low current on the points causing them to become contaminated but nobody has mentioned it here
Dennis and I are trying to stir the pot
Jim

Okay, thanks Jim.

I started driving my XK120 DHC in 2000. I drove it until 2013, over 21,000 miles before my rebuilt original AUA31 flat topped cap, square body SU fuel pump packed up. This pump was on the car when I got it in 1974. I replaced the points with dual points and diaphragm way back then to get the car going, but never drove it until I restored it and made it drive able in the late 90s.

Unbelievably, the car never missed a beat during this time after I started driving it until the fuel pump died at home in my garage. Didn’t leave me high and dry.

This was the basic original type SU fuel pump without a condenser. So it arced and sparked for all that time and all those miles.

I’ve had several failure with replacement pumps since then, one of them on the New Jersey Turnpike of all places! Something to be avoided.

The next generation of SU fuel pump added a condenser in parallel with the points, the AUA52. This reduced but did not eliminate the arcing and sparking. But it was a step forward.

Since then, SU made another improvement by replacing the condenser with a varistor some time around 2010 I believe. I have literature from them that describes them around that time.

From Google:

A Varistor is an electronic device with a “diode-like” nonlinear current-voltage characteristic. A major function of varistors is to protect circuits against excessive transient voltages. They also conduct a great amount of current when voltage is excessive.

Within the past year, I tried to purchase some from Burlein Fuel Systems, the UK SU company. None available. They were quite vague in their communication about the device and it is now called a suppressor. They said the had some on order and would contact me when they were available. Six months went by. Then the contacted me by email to confirm that I still wanted them and I said yes. The part number is CZX 104 and again it is called a suppressor.

I ordered 6 of them and they cost 7.07 BP ea.

They have an identifying part number on them that I again googled. Turns out they are called ESD suppressors, TVS diodes, and bi-directional. Works on positive or negative ground because they are designed that way.

“ESD suppressors are semiconductors that protect electronic components and systems from electrostatic discharge (ESD), the sudden and uncontrolled transfer of an electrical charge between conductors. They are installed near the protected line and connected in parallel with the signal line.”

I bench tested one on my original “sparky” fuel pump and saw ZERO arcing and sparking.

I dug out one of the older type varistors that I recently acquired and just like the old condenser/capacitor, it sparked occasionally.

So what we have here, is, I think ,an elegant alternative and upgrade to the standard points type SU diaphragm fuel pump. Just add this two wire suppressor across the points, and from what I know now, the pump should not fail because of points breaking down. The other mode of failure, the hardening of the diaphragm, should be the main mode of failure and that takes many years.

BTW, this suppressor is simply a resistor like looking tube, about 3/16" in dia. and 3/8" long with a wire on both ends with terminals on the ends. One end goes under the a pedestal screw and the other under the points blade. It fits under a flat cap with no problem as it can be bent down out of the way. Simple, looking but a complex electronic device.

Voila! Keeping my fingers crossed and hoping for the best. I will put the original pump back on my car and put a “suppressor” on the spare that I carry (and have had to use too often). I’ll see how it works out and report back when I have some miles on it.

John Brady
678462

2 Likes

Good report Thks for the info

Jim

Last time my car wouldn`t start , I realised there was no ticking sound coming from the rear , so , open the boot and give the pump a few light taps with a small hammer and , voila , turn the key and a rapid ticking can be heard and car starts ok . Since then I replaced the old SU with a small modern item which runs continuously and is a bit noisy , but hopefully better than the 50 + yr old SU .
So , was the problem the points , or something else ?

Almost undoubtedly, the problem is with the points. If you want to go back to the SU, you can either do the transistor trick, or convert to full electronic triggering. The pumps themselves were quite robust units.

2 Likes