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MG TD TF 1500 - Transistorized Fuel Pump - Question to Dave DuBois

Dear all, but especially to Dave DuBois:
This is a Question to Dave but I think it is of interest to many other readers.
I’m just in progress to rewire my fuel pumps to the transistorization suggestion I found here:
http://www.mgccq.org.au/tech4.htm
My question is linked to the wires I found when I open Bakelite Cap from the pump. I refer now to the Picture which is enclosed to this posting.
Starting from the left side, I can see the following wires:
• A red wire coming from inside the pump and going to the terminal fig.: 1, #5
• A black wire coming also from inside the pump and going to the stationary point fig.: 1, #1
• A green wire coming from a blue capacitor and going also to the stationary point fig.: 1, #1
• A brown wire coming somewhere from the contact mechanism to the screw fig.:1, #2
• And again a green wire coming from the capacitor again and going to the screw fig.: 1, #2 as well.
My question now: Do I need the capacitor or is it superfluous?
Thank you
Cheers,
Guenter



GK Guenter

Guenter-
I don't have an answer for the design in question. If I am not mistaken Dave D now has fully electronic pumps (no points) available, too. Somehow I missed that article from the Queensland Club.

Another scheme for prolonging the life of points is written up by the John James British T-Type publication. For anyone interested, it uses one "transil" or TVS diode that keeps the points spark from getting too big. I installed one a few years back. The transil used is a sort of diode, but it can be hooked up either way, and makes the pump pos or neg ground--so it can be hooked up either way. These were being offered through the t-type article-- already made up with connectors soldered to the leads, and sized to fit. Not sure if they still are available like that.
http://ttypes.org/ttt2/?s=transil&submit=Search
D mckellar

Guenter - Yes, that is an article that I wrote many years ago. If you remove the two green wires going to the varistor that they come from, the wiring left will resemble the drawing in the article that I wrote those many years ago. If you want to proceed with the transistor, go ahead with the conversion, but first read below as to why this approach doesn’t work as well as I had hopped for and why I went to a system that completely eliminates the points.

That modification that I came up with those many years ago did, in fact stop the erosion of the points contacts due to the electrical arching when the points open, but the unintended consequences is that with the suppression of the arching is that there is nothing to burn the film that develops on the points contact. The bottom line is that the problem of the points contact erosion due to arching is replaced with a build up of the film on the contacts that results in the points not conducting the needed current through the coil - stopping the fuel pump from working. The installation of the transistor just replaces one problem with another different one.

The latest approach for solving the problems of the points from erosion from arching by Burlen Fuel Systems is the varistor that I mentioned above that reducing the arching across the points sufficiently to prolong the life of the points, while maintaining sufficient arching to keep the film from building up to the amount that the points contacts wind up being insulated one from the other. The suggestion from D mckellar of using the TVS diode will work about the same as the transistor modification or the use of the varistor and is easier to install than the transistor.

The other thing that Burlen Fuel Systems have done to increase the reliability is to produce the pumps is to use a Hall effect (magnetic triggering) circuit to completely eliminate the points in the pumps. This approach works very well as long as the Hall mask is adjusted correctly. At the same time I started using an optical trigger, using a vane soldered to the lower points trunion that breaks a beam of light. This approach has worked equally well as the Hall effect circuit, but costs less.

If you are interested in modifying your SU fuel pump with either the Hall effect circuit or my optical trigger system, e-mail me at Sufuelpumps@donobi.net and I will give you the part number of the Hall effect circuit from Burlen Fuel Systems or the name and contact for a gentleman in the Netherlands who restores the SU fuel pumps using my optical trigger system. Cheers - Dave
DW DuBois

This thread was discussed between 14/10/2016 and 15/10/2016

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