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MG MGB Technical - Noisey Fuel Pump MGB GT (75)

Hello All
Great forum by the way just found it. I have recently bought the above car. It has just passed the MOT but since the car stutters badly under 2000 RPM. I have had a garage spend about 2 hours on tuning the carbs so as to pass the test. Please does anyone have any ideas as which route I need to follow? Do I need new carbs or is it the engine?

Any help would be appreciated.

K Regards
Ian
Ian Rowland-Hill

Sorry alsoI forgot to mentoin but I have a very noisey fuel pump. It has a very loud hummm to it from the time the key is turned on? I have been told this is due to low fuel but there is plenty in the tank?

Any ideas? Is it on the way out?

Thanks again
Ian
Ian Rowland-Hill

Ian
The fuel pump if a standard SU pump at the rear of the car underneath by the tank should tick when you switch on the ignition it ticks till the float chambers at the carbs are full and then stops, it will tick when it tops up the float chambers from then on. Check the delivery by taking the feed pipe off at the engine bay carb end and see how much it delivers into a recepticle when an assistant switches on the ignition. Check the archives on this board for the amount you should be getting, Once satisfied the pump is delivering enough to the carbs turn to the other places you need to check out. Ignition timing and points settings and plugs must be checked and valve clearances must be set up correctly before fiddling with the carbs.
As you have only just got the car the carbs are an unknown quantity so they may be worn and no amount of tinkering will get them right so you need to check out if they are worn.
Throttle spindle bushes do wear out resulting in air being sucked past them weakening the fuel mixture and preventing an accurate set up. Have a look in a Haynes manual or search the web for SU Carbs, you will find some very good pages to guide you through tuning the carbs. Have a look at Paul Hunts site
http://www.mgb-stuff.org.uk/
click on spanners and this should explain all you need to know.
I had similar problems to you except the pump was ok on mine just carbs worn out, I got a second pair off ebay and had those rebuilt, not cheap but boy were they good when I put them on the car, set up was text book and took me very little time.
Hope that helps

Colin
C J Bryan

Ian - It sounds like the previous owner installed one of the small, square, run all the time, make a lot of noise, Facet pumps in your car. These pumps run constantly regardles of the needle valve in the float bowl being shut off and since they are hard mounted to the chassis, are quite annoying as the noise is transmitted directly into the passenger compartment. That said, these are a good pump and are as reliable as any other pump. Check the delivery rate as Colin suggests. The pump should deliver close to 2 pints per minute (that is US pints, you will need to convert to Imperial pints).

If the noise is a problem to you, there are two different routes that can take to correct the noise. First, convert back to the original SU fuel pump (You will want one of the AZX 1300 series pumps), which are sound mounted when installed properly. If you go this route, I would suggest leaving the noisy pump in place, plumb the two pumps in series (both have check valves in them and will pump throught one another) and wire both pumps to power through a single pole, double throw switch. This way you will have a permenantly installed back up pump that will get you home witht he flip of the switch if the primary pump should fail, where you can repair the offending pump in the comfort of your own garage. The second route, is to sound mount the existing pump. Sound mounts are available from Pegesus Racing. Go to the follo9wing link, http://www.pegasusautoracing.com/advcat.asp?CategoryID=AIRFUE
click on Fuel Pump Accessories and scroll down to Facet Mounting Kit. The installation of this mounting kit makes the pump quiet enough that it can't be heard above the engine at idle. Good luck - Dave
David DuBois

Most running problems are in the ignition system rather than the carbs. Try checking the plugs, leads, points, condenser and distributor for good function, and replace any bad components.
dave

Ian. You mention that you had a garage spend two hours tuning the carbs, then, ask what direction you should proceed in--engine work or more carb work. I should think that any qualified mechanic should be able to tell you the condition of the carbs, and give you a good idea of the general engine condition if he had just spent two hours working on it. If he cannot provide proper guidance to you, you need to take your car into a proper specialist and have it checked out and tuned.

Generally speaking, most of us would run a compression check (both wet and dry), check and set the valve clearances, inspect/replace the points and condensor, (cleaning and lubeing the dizzy while it is out), set the ignition timing and, if we had one, use a vacuum gauge on the intake manifold to see what it could tell us. Paul Hunt's website, listed above, has a lot of information on how to do much of this. My website, www.custompistols.com/ has an MG section with tech articles which will also help you understand what needs to be done and what you should be seeing. (There is also a fuel pump article by Dave DuBois which might prove of use for figuring out what your existing pump is.)

A specialist would perform all of these checks and check out the engine on an engine analyzer which would allow him to have a visual read out of the sparking voltage of the spark plugs, cylinder balance and a few other areas which only the more expensive (beyond what most hobbyists can afford to buy for casual use) test machines offer.

With the results of such testing in hand, it is fairly easy to decide what areas might need attention and how long you could put off such attention. (In other words, it allows you to come up with a list of things which need to be fixed to drive safely, followed by what needs to be done to make the car reliable, then a list of "nice to have/will need doing soon" type things to be done as time and finances allow.) As it is, we cannot offer a great deal of assistance. With the test results before us, we can, in effect, sit down and talk with you about what they mean and what we feel should be done.

Les
Les Bengtson

This thread was discussed on 26/06/2005

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