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MG MGB GT V8 Factory Originals Technical - Electric or mechanical fuel pump?

I obtained a good Rover 4.2 engine for use in my conversion ... it came with a mechanical fuel pump ... is there any reason not to use it, but to fit an electric unit instead? (I know, you guys like 3.9s, but the price was right and the thing is practically brand new, plus come on the stroke is just a frac longer on a 4.2) Seems to me that, yeah, a mech pump probably hogs a couple of HP, but it would be more reliable. Or am I missing something? (This will just be a carbureted car, with hopefully a Carter 400 or if I can't find one an Edelbrock 500 ... (I am not a Holley man, I hate those things) ... anyway the SU fuel pump from the 4-banger probably isn't even close to the required fuel pressure, which IIRC is 5-6 psi ... plus those pathetic pieces of crap are always breaking down ... so it's either replace it or stick with the mech).

Also, I am not too patient at plumbing ... can I just use my old 5/16 fuel line, or do I absolutely have to go put 3/8 on there?

I really respect you EFI guys. If you have the patience to rig all that stuff up correctly after the 9,998 other things you did to get the V8 in there, my hat is sure off to you. Discretion being the better part of valor, I will just do the Bronze Age thing and hook up a carb.
Tim Patterson

I now have a total of over 400,000 miles of MGBV8 driving under my belt, in 2 cars, in over 14 years. Both had or have stock SU 4 cyl electric fuel pumps. They last, on average, about 120,000 miles, although I had 1 fail in less than 1000 miles. They have been adequate for a built 215, sort of stock 4.2, in all circumstances except 4th gear in an all out drag race. Slightly fuel starved above 95 mph, but only in a drag. I run both 400 & 500 cfm Carter carbs. I also use the stock fuel line.

I have installed a back up pump, one of those noisy square things, & do use it in the very infrequent drag race by flipping the on/off/on switch to the other side. These cars are daily drivers for me, so the second pump is a security blanket.

Can't speak for other combinations, but the Carter is a very flexible & forgiving unit.

Jim Stuart

I plan to stick with the stock SU for the time being. It probably does need help at high RPM, though. Also I'm running a 3.5L.

<<plus those pathetic pieces of crap are always breaking down >>

I can't agree with that. I have had my MGB for 13 years with no fuel pump problems. Okay, I did have to tap it with hammer one Spring after sitting all Winter. Normal.

My Dad's '63 MGB (original owner) with 180,000 miles (yeah, the one that I drove to the Cleveland MGV8 meet) still has the original SU fuel pump. One set of points in 37 years. Not too bad. :)


Sounds like you have had great luck. I've gone through a few of them on my 4-cyl. cars. But what's the basic disadvantage of a mechanical pump?

I have been having problems with the fuel pump, even though it has been serviced recently.
When I first start the car after a week standing, it will start ok first time but the second time, after 10mn or 1/2hr running, it will generaly need a few whacks with a hammer to get going again, but the last couple of times it has taken a good 1/2 hr of bashing to get going again.
I've heard of "solid state" fuel pump which should be a lot more troublefree.
Has anybody heard of these? Are they better than new O/E? and who makes them?
Thanks for any infos,

cazzola - the benefit of the 'solid-state' (it is actually a conventional reciprocating pump but with electronics in place of the points) is said to be that there are no points to stick open or closed. However, if they do fail you can usually do a quick-fix at the road-side, whereas if an electronic unit fails you are stuffed. Who knows how reliable the solid-state units are? I just know I have had intermittent problems (the worst kind) with mine. I carry a points-type as a spare.

Paul Hunt

I can only agree with the other V8' ers. I have a 3.5 Rover in the car and still run the original SU pump. Have now about 350.000 miles on it and not one failure.also run the Carter 500 cfm from Towery. Very good results!
There is a guy in WA state who can repair your old SU fuel pump very professionally. I think the costis around $50 depending on te parts he need to restore yours. He doesn't recommend the electronic type conversion. Will see if can find his address.
ood luck with your conversion. 4,2 should give you plenty of power!
Werner Van Clapdurp

What's the disadvantage of using a good old fashioned mechanical pump ... the kind attached right onto the motor?

Some disadvantages of the engine mounted, lever operated pump are: (1) The pump is a long way from the tank and in a hot place, making it more prone to vapor lock. Pumps are more efficient pushing than pulling fuel. (2) The starter has to work harder and longer to get fuel to the carbs should you run out of fuel or experience a drain-back problem. (3) One failure mode of the mechanical pump is for the diaphram to leak fuel into the sump, diluting the oil and opening up the possibility of a sump explosion. Another failure mode is for it to stop pumping with no warning signs, something that seldom happens with points operated electric pumps. I've never been able to persuade a mechanical pump to get me home by banging on it.
George B.

This thread was discussed between 05/12/2000 and 19/12/2000

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