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MG MGB Technical - Replacement Fuel Pump

After looking and looking for a reason for my high speed skip I have discovered it is my fuel pump. How did I find out? It got worse and worse until it quit. I have removed it and cleaned and reset the points twice but it still does not give adaquite flow.
Question: should the replacement non SU pump be below the tank or can the new electric pumps pull the fuel to the engine compartment?
Ken Knize

Hi, Ken - you don't say what year your car is, but the average delivery for an SU fuel pump as used on 1098 and 1275 cars is over 8 gal/hr (which, based upon 30 miles-per-gallon works out to over 240 miles-per-hour). Whew! During this time, the pump will be ticking like mad, something between one and two ticks-per-second.

But, if I read correctly, you're asking if you can mount the new ("non SU") pump in the engine compartment, or if it has to go in the general area where the old one was. Many of these pumps have poor "suckability", but great "pushability". Mounting up front would mean drawing about a 16 inch "head", plus it would be through several joints and about six or eight feet of line. Any pinhole leak along this length would kill your fuel delivery.

Safety says leave it toward the back, but that's just my opinion. You won't really know 'til you try. Best of luck - - Alec
Alec Darnall

As Alec says you have to put things like Facet fuel pumps near the tank rather than in the engine bay. As for above/below. Doesn't really matter as far as I'm aware - in my case (an escort mrk2 tank) the fuel comes up and out anyway so unless you have the pump much lower to act as a siphon (impossible in my case due to ride height) then above/below is the same deal.
Stefan Carlton 1


my fuel pump took a dive on my 79 MG-B. The points were toast as was the entire unit upon closer inspection. I replaced it with an electronic unit which fit form and fashion in the same space as did the original. The unit looks the same as the old right to the hose and electrical connections. Replaced all the fuel hoses as well - very important item.

cheers

Gary :>{D
gnhansen

Was the pump ticking a lot? If so, maybe it ain't the points. Maybe it's the IN-OUT reed valves.
Daniel Wong

Thanks for the good words of advice. The car is a 73 chrome bumper, low compression, non OD. Engine seems sound, good compression. New dual point dizzy. Peco, Peter Burges recomended exhaust. Carbs rebuilt new air cleaners w/correct needles. This has been a 5 year summer project when I'm not touring the USA in my 5th wheel camper. As my retirement years advance it's more and more difficult to get under the car, to say nothing about getting back up again. From what you have offered I guess I'll have to place the new fuel pump under the car, or try to find a shop that can help with it. I think I'll leave the old pump in place so that if the car goes to a purist some day thay can convert back to old system.
The pump was pumping or ticking very slow then not at all. My first attempt gave me 5 ticks befor it quit. Now ticking slowly and if I goose the engine it responds well until the carbs run out of gas the she breaks up badly until the fuel is replenished.
As I write this I,m wondering about a cloged fuel filter, I'm going to look now.
Ken Knize

Well, I'm not so sure about the fuel pump. I took the fuel filter out and tried to see how much flow I got. Cannot measure the flow but it would have filled the quart can in a few min. Not a forcefull flow but it seemed considerable. Put in new filter car runs the same but does not seem to have the exact reaction. Now it just seems to break at 3500 to 4000. I think, I had a fuel pump problem that I have corrected now I'm back to the same high rpm skip. If I keep the rpm's down (what fun is that?) she runs like a new car, couldn't be smoother. If I goose it she breaks up. Her name is "Ruby" I hope she doesn't mind being goosed.
I'm going to start a new post "High RPM Break up" see you there.
Ken Knize

Ken - The original SU fuel pump in that car should pump a bit over 2 pints per minute. Before going on to something else, I would put a mark on the container you were using before at the 2 pint level and try pumping fuel into it for exactly 1 minute, then see if you got to the 2 pint mark. If not, you are probably going to need a new pump. If you are getting the 2 pints per minute, then you need to look elsewhere for the cause of the break up. Cheers - Dave
David DuBois

Hi Ken,

In the last week I have suffered the exact same problem. Initially the problem was just at high speeds - if I travelled at over 90 mph for more than a couple of minutes the power would just bottom out. If I then pulled over and slowed to 70 for a minute or two and allowed the pump to catch up it would be fine again and I could climb back up to 90 for a while (if it had been an ignition problem I am assuming that the problem would always have been present at or above a certain number of revs).

Last week the pump gave up altogether. It was the plastic SU looking type. Rather than try to renovate the pump I have bought a new cylindrical Facet solid state pump which I am fitting tomorrow. I will let you know how it goes. I temporarily hooked it up yesterday without mounting it to the body and I saw a good strong gush of fuel into the filter and once the pump itself was full of fuel it didn't sound too noisy at all (some people are irritated by the noise).

Sorry I couldn't have been more help earlier before you pump also gave up.
Alec

The problem you describe could be ignition related, as carb problems often are.

If it passes David DuBois's test check your points condition and gap (or dwell), plugs, and conections to the coil etc. Look for sparking round the HT leads in the dark and try swapping the coil with another.
David Witham

Thanks for the feed back. I couldn't possibly get neer 70mph let alone 90. If I verrrry slowly increase speed I can get 55.

I do think Its ignition related now not fuel pump. Daves test was a little of the mark but not much. I cannot get Moss to respond on the Petronix, I felt safer going to them as that is where I bought the dizzy. If I had a problem I would prefer to go to first person.
Ken Knize

This thread was discussed between 07/08/2005 and 10/08/2005

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