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MG MGB Technical - New fuel pump - richer mixture?

My 63 MGB had an unoriginal, German made electronic fuel pump, I believe the brand is Hgo or something similar. Some days ago it stopped working after ten years, so I replaced it with another German made electronic pump. The brand name is Hardi, in a Quinton Hazell branded box. Judged by the weight and outside finish, the quality appears to be very good.

Now it seems to me that the fuel mixture is a bit richer than before. I have not looked at the plugs yet, but the engine feels a little uneven when I am cruising in top gear at low revs, and the general feel has changed a little. Performance at higher revs is excellent.

An article in the latest edition of MG Enthusiast mentions that some generic electronic fuel pumps gives a higher pressure than the original S.U. pump, and that this forces the needle valve a little, giving a slightly higher fuel level in the float chamber. If this is the case here, I will probably have to adjust the carburetters to give a weaker mixture?

Has anyone else experienced something similar?

Tore
Tore

Adjusting the carbs is the wrong way to approach this problem. You will not be in a controlled state if you do that. Personally I would either change the pump, or fit a pressure reducing valve, but not one of the circular diaphrgm stlye. I posted some pics here of mine after it split and pumped neat petrol over the exhaust manifold.
Stan Best

If the old pump was causing some starvation but the new isn't, or the new pump is too high a pressure and causing flooding but the old wasn't, then it's possible. However the former would be characterised by stumbling on acceleration, and the latter by leaking from the carb vents if the ignition is left on for a while with the engine stopped and coil disconnected.

As Stan says maladusting the carbs is NOT the way to go in either case, I'd rather fit a correct pump than a pressure regulator which is something else to go wrong/leak.
PaulH Solihull

Tore. Put a fuel pressure gauge on the line going to the carbs, disconnect the wire from the ignition to the coil and put a piece of tape over it, turn on the ignition switch and read the actual fuel pump pressure. Dave DuBois indicates that the current SU fuel pumps, sold for use on the MGB, may have as high as 3.8 psi pressure and seem to work for the SU carbs. If you have more than than, a pressure regulator or pump change is in order.

Les
Les Bengtson

Strange things are happening. I did some research on the web yesterday, and found specifications for the QH pump I have just installed on Barney Gaylord´s MGA website:

http://www.mgaguru.com/mgtech/fuel/fp205.htm

According to this, the pressure of the QFP 172 E pump that I have is 4.4 psi, so clearly excessive. Just as an experiment, I tried yesterday evening to adjust the carbs a little weaker, just two flats. When cruising at 30 mph in 4th the engine was running even more unevenly than before.

I also looked for leakages, to see if the float chamber valves was letting fuel through. No fuel running out, and the pump was not clicking. But later in the evening, when I started the MGB after a short run, the fuel pump started clicking like mad as soon as I switched on the ignition, as if it was running in air. I switched on and off a couple of times, no change.

I am now inclined to change to an SU pump, even if it will mean some extra work to make the original bracket fit, because I believe the mounting has been modified on my car.

But I wonder what is happening here? Could the uneven running be caused by something else? And why is the new fuel pump suddenly running wild?

Tore
Tore

Hi, Tore, I've been running my 1964 MGB on a Hardi pump for the past 18 years with no problems.

It has been far more reliable than the SU pump it replaced. There was an after market pump, made in Australia, on the car when I got it. It didn't pump enough petrol so I replaced it with an SU pump. That gave up after a year or so.

Wild running pump: Your pump may be sucking air in. I would check the connections on the pump on the suction side. They could have come loose. The other possibility is that the fuel line has perished and needs replacing. The ethanol in the fuels these days is causing problems.

Mike
Mike

I have been having lots of fuel pump issues and of course sucking air on the intake side is a common problem but I have also found that bleeding the lines helps. Disconnect at the carburettors and allow the pump to pump some fuel into a container before reconnecting the fuel pipe.

Of course make sure your fuel filter is ok if you have one.
Ian Buckley

When I installed the new pump I managed to mix up the inlet and outlet pipes, so for a few seconds it pumped fuel FROM the carburetters INTO the tank. Could that have caused air pockets in the tank line that I can bleed out by letting it pump fuel into a container as you describe? And can that be the reason why it is running wild?

Tore
Tore

Certainly an SU pump should be capable of correctly filling the carbs even if the tank, pump, pipes and carb were completely dry previously, without bleeding, can't speak for other brands. Air anywhere forwards of the pump will just be pushed out of the vents in the carbs when the floats are low enough to open the valves.

Switching off a hot engine on a hot day can allow heat-soak to evaporate the fuel in the carbs, under those conditions you can hear it boiling on my V8. Restarting after that does cause the pump to chatter like billy-oh for a couple of seconds, but only that, and it soon starts slowing down. Could be coincidental like an air-leak on the suction side as mentioned, or maybe they just aren't as reliable as they used to be like so many other things and the new one has prematurely failed - e.g. a stuck inlet valve (if it has one)
PaulH Solihull

Tried to bleed the fuel system as Ian suggested. It worked, and the fuel pump capacity is quite good. But the clicking of the pump was a little irregular when pumping into the container. Could that indicate a bad electrical connection?

Tore
Tore

While we are on the topic of fuel pumps...

I replaced my little brass block fuel pump, mounted on the ledge next to heater box on my 72B; with a Carter universal fuel pump (P60504DP, I think $50-$60) - with in line filter.

I relocated the Carter fuel pump back to the original location by the right side of the fuel tank.

I made sure I bought a Carter pump with the appropriate pressure range.

I think the pump is working fine, but of course I read the above and I hear others talk about the pump clicking, with reference to the rate of pump clicking; and now I'm paranoid again.

The old brass block pump, was a constant fast clicking pace and sound. The carter, being further away is of course quieter, and a little less clicking.

But it always is clicking. When I turn on the ignition the rate I hear is the same as when it is running down the road.

I've heard people make references to only hearing the pump when they turn on the ignition, before starting the engine; and some commenting that they don't hear the clicking if the car has already been run that day.

I always hear clicking, same rate whether at idle, pre-starting, or going down the road. To me this makes sense - using fuel, pump clicks.

Don't tell me I have something else to be concerned about! I no longer have a clear fuel filter up by engine (pre-carbs) so I cannot observe fuel flow, the filter is back by pump, pre-pump.

Please tell me I can ignore the rate of clicking!
R.W Anderson

Fuel delivery should be greater than one Imperial pint per minute (with a fuel hose removed from a carb and directed into a container) and in practice more like 2 pints. For an SU at least this should be in a steady and regular series of pulses with minimal bubbles.

SU pumps only click when there is a demand for fuel, some aftermarket pumps are the same, others click all the time ('demented woodpecker' has been mentioned) the ignition is on regardless of demand. From comments found on Google the Carter does seem to make a continuous noise as it as rotary and not a reciprocating like the SU, although more of a whine than a clicking. Many comments complain how noisy it is.
PaulH Solihull

Thanks Paul.

Demented woodpecker it is!

It isn't as loud or "demented" as that little brass block pump I carry as a spare now.

I liked the 10,000 life expectancy of the Carter (or something in that range - which exceeds my entire remaining driving time in life - I think!) and the relatively low price.

With all the other noises, including the exhaust sound created by essentially using a FarmAll tractor muffler - the top down - & stereo going; the fuel pump sound is hardly an issue, at least I know it is working.

And in hindsight, you are correct; the comments on the pump not clicking after a few minutes or if car was run earlier that day was referring to a B with original SU pump, not aftermarket.
R.W Anderson

Tore,
I have one of those Hardi pumps. I find it clicks a lot especially when I accelerate. Lots of clicking at switch on to. I find it has two tones. A much more pronounced click as if it were pumping air and a more subdued one which is what I would expect if it was pumping fuel (takes longer for the diaphram to move). I expected to see flooded carbs and an engine bay full of fuel but I've had a couple of tanks of fuel through the car now that it is back on the road and it doesn't seem to be guzzling fuel. The pump was fitted by the P.O. I must look for the part number on it to find out if it is delivering the correct pressure.
Steve Church

That is interesting, Steve. That matches the different sounds I heard from the pump yesterday. Just going out to the MG now to turn the key with trembling fingers and see what happens...

You may have trouble finding the part number on the pump, I only found it on the box.

Tore
Tore

Tore. With 4.4 psi of fuel pressure, the addition of a fuel pressure regulator to the existing system would be worthy of consideration. Changing to a new SU fuel pump is an alternative, a quite viable one to me as the pressure regulator adds another piece of complexity to these simple cars. And, to me, the simplicity of the vehicles is one of their most attractive features.

There is, however, another area which no one has bothered to touch on here and one which cannot be corrected through the use of a fuel pressure regulator or new fuel pump. Specifically, you note in your first post that the problem is most evident "at low rpms in 4th gear", or something to that effect. Later, you mention: "I tried yesterday evening to adjust the carbs a little weaker, just two flats. When cruising at 30 mph in 4th the engine was running even more unevenly than before."

I normally shift into 4th gear at about 40-45 mph. Sometimes, I will shift into 4th at 35 mph when that is the speed limit and I have several miles to drive at that speed. However, using 4th gear for 30 mph is just not desirable in my experience. The engine is not yet getting into its power range at about 1,950 rpms--the engine rpms for 30 mph in 4th gear. My experience is that running the engine at such low speeds will cause you to notice the engine running roughly/poorly because it is below the bottom end of the effective power range in the gear that puts the most loading on the engine when below the power range.

Thus, I suspect part of your problem is the driving style as much as the slightly high fuel pressure being delivered and am interested in hearing what the others have to say.

Les
Les Bengtson

I don´t usually drive 30 mph in 4th for long distances, I just know that when everything is in shape my MGB is capable of doing it very smoothly, and that is not the case now.

I still consider both possibilities - keeping the Hardi pump or changing to a new SU. I m not sure if the mounting bolts for the SU pump bracket is in place on my car, will have a closer look underneath this evening.

If I go for the Hardi, where would be the best place to put the fuel pressure regulator?

Tore
Tore

All problems solved! I decided to do it the hard and expensive way, and install an SU AZX1307 pump. A lot of trouble, but well worth it.

The decision was made when I took out the spark plugs and noticed that the plugs in cylinder 3 and 4 were black, cylinders 1 and 2 light brown. Last time I had them out they were equal. This matches exactly what has been said about a pump with too high pressure that overwhelms the needle valve, particularly in the rear carb.

When the SU pump was in place the engine ran noticeably smoother. The thought then struck me that if the Hüco pump that has been in the car since I bought it also had too high pressure, that may explain why I have not managed to get a really satisfactory carb adjustment. So I did a complete adjustment from the bottom up. Now the car runs better than it has ever done! It also feels quite a bit faster, but that may be subjective.

Information on the web shows that the Hüco 13 3000 pump that was in the car before gives 4.4 psi pressure, exactly the same as the Hardi/QH QFP172E I first replaced it with. Yet the car ran better with the Hüco than with the Hardi. Maybe the pressure on the Hüco was lower or the Hardi is higher. But as I said it never ran as well with the Hüco as it now does with the SU.

I never thought fuel pressure was that important. And I doubt if many of my local MG friends know. I will clearly write an article about this for our "MG Magasinet"!

Tore
Tore

This thread was discussed between 04/07/2011 and 09/07/2011

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