MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - fuel pump pumping when engines not runing?

hi all just a couple of quick question i have a 1970 mgb is the fuel pump supsose to keep pumping when the engine is not runing?

my oil pressure shows around 60 when the engine cold at idle but once warmed up it drops to around 20 car seems to drive ok and docent smoke so what could this mean?

lastly the gears steam a little stiff to me are all b,s like this changes gear ok but can be a bit of a pig to get into reserve i normally have to hit it across to get reserve.

thanks in advance steve

s truman

Steve - I'll leave the other questions to others, but the fuel pump should definitely NOT run when the ignition is shut off. It sounds like someone has run the wire to the fuel pump to the wrong side of the ignition switch. It should be on the white wire circuit, which is switched, unfused. Go to: http://www.advanceautowire.com/ Click on Stock Schematics, then MGB and then scroll down to the proper diagram for your car and print out the diagram. You can copy the entire file and take it to a copy shop and have them print a full sized (14 X17) print and laminate it for future use. Cheers - Dave
David DuBois

the fuel pump pumps with the engine turned off and the ignition light on?
if i turn the ignition off the pumps stops is this normal?
thanks for the web address to.
s truman

Steve,
Ignition off pump should not work
Ignition on, engine stopped the fuel pump clicks only for carbs. bawl filling stage at engine statup, no longer. If is clicking on more than 10", you may have a leak onto either the pump succion side or the outlet side.
Oil pressure is OK at cold, but a bit low when warm. Practical classics states, it should not drop below 45 psi at idle when warm.
Stiff gears is not that important provided the gears shift correctly.
Regards.
Renou

Do you have the original type SU pump or has a PO fitted a Facet pump or similar? Some of these pumps click continuously, even when no fuel is required.
Dave O'Neill 2

thanks for the imfo so far guys
the car has standared twin su carbs i,l have a look for leeks just as a mater of course.

as for the oil pressure ive made a cock up!

when the engines hot and driving the oil pressure drops to 10 witch does seem quite low.
with engines hot at adle its around 40
engine cold its at 60

also just come back from a run and the wife said it was blowing quite a bit of black/grey smoke.
s truman

The pump is powered with the ignition on, regrdless of whether the engine is actually running or not. However with the ignition on but the engine *stopped*, the original SU pump shouldn't click more than once every 30 secs. Any more frequently than that could be a float valve leaking, in which case you will have fuel dripping on the ground from one or other carbs, or possibly the one-way valve in the pump is leaking back.

But some after-market pumps do whirr or click all the time and it isn't a problem, so you first have to find out what type of pump you have.

From your first post 60 cold idle and hot or cold running is normal (50 to 80 is the range), 10 to 25 hot idle is the range given in the Workshop Manual. I'd consider 10 very low though, mine normally hot idles at around 40, only dropping to 25 if stuck in traffic on a very warm day. 20 hot running is very low, could be the pressure relief valve needs reseating.

But your 2nd post doesn't make sense - hot idle is 40psi, but hot running is 10? Something very wrong there!

Black smoke is usually rich mixture, oil burning is usually blue. White/grey is coolant.

Sounds like you are new to MGBs. They are very different to modern cars, most things are usually heavier and harder. Reverse has a spring-loaded detent rather than something you lift up or press down to enable you to go into reverse, so you do have to knock the gear lever across the gate to get it into position to pull down into reverse, you would need to push pretty hard without that. Other than that unless the clutch is dragging (grinds when selecting reverse) selecting forward gears should be easy and smooth, better than some more modern machinery.
Paul Hunt

i,l have a check on the oil pressure again and right it down this time, i may well be getting it wrong.

with the engine running i cant see any petrol leeks as such but there does seem to be a after market fuel pump fitted

ive had a few mgb,s but this is the first one i have had on the road, ive always lost interest and sold previous cars before ive completed rebuilding them.

i know what you mean with reverse gear i have to hit it across with my had and then pull it down.

im not to worried about the smoke at the moment, it is an old car after all and it does seem to drive ok
i report back after next time im out at right down the oil pressure again.


s truman

If there is black smoke when running and the pump keeps ticking when the engine is not running, the float in one of the carburettors may be leaking.

Pull the oil dipstick, if the level is high and the oil smells of petrol, the petrol is leaking into the sump. Change the oil if it is polutted by petrol.

Check the sparkplugs, if a (left or right) pair is blacker than the other pair, you have spotted the faulty carburettor. A Haynes manual may be helpful to see where everything is. If the float is leaking you will see or hear petrol sloshing about in it.
Willem van der Veer

ok checked the oil no smell of petrol but is on the minimum mark so has used a little oil since last time i check.
also had a look at the plugs the 2 near the front of the car look very lean or colour less, don't know how they should look.
the 2 near the heater box have more of a slight brown tint colour.
not driven the car sine my last post but oil pressure is 50 at idle just under 60 when revved.
s truman

The small difference in plug colour indicates the carbs are unbalanced - the whiter pair being weak, although with unleaded the colour indication is less helful than with leaded.
Paul Hunt

This thread was discussed between 18/07/2009 and 21/07/2009

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.