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MG MGA - Fuel pump + fuel filter sequence

I am sorting through some fuel pressure problems this Spring taking my 'A' out of storage. I've had the car only one season, and it ran pretty good last year, but with a pretty rich mixture.

Anyway, upon startup this season, further investigation reveals that an aftermarket pump with high fuel pressure (~ 7 1/2 psi) is installed without any fuel pressure regulator.

The symptoms are that occasionally, the fuel bowl overflows. The carb seats and seals have all been recently replaced. Can you confirm that high pressure alone would cause this?

Also...I've read on the forum that the proper order for fuel pump + filter is for the filter to be on the downstream side of the pump to avoid burning out the pump due to a clogged fuel filter. However, researching replacement aftermarket fuel pumps, I find that the Carter 60504 is an application that is recommended. I have attached a picture of the Carter package. It consists of a fuel filter and inline pump. Clearly the filter is on the input side of the pump. Isn't this contrary to the previous advice?

Any thoughts?

Thanks,

Rick



rpb bunch

The advice about no filter before the pump is specific to the original fuel pump. I you are using this setup the advice does not apply.
R J Brown

Yes it contrary to the previous advise but after the pump is where it is supposed to go on these cars. If your pump is producing 7 1/2 lbs then you will need either a new pump or a fuel pressure regulator which will take care of your problem.
Good luck
Kris
Kris Sorensen

Rick,

Do you have a fuel filter at present? High fuel pressure could cause the bowls to overflow, but small particles in the fuel are more likely to be a problem.

The advice not to have a filter on the inlet side of the pump is specifically for the SU pump. Other pumps may have their own requirements, depending on their design.
If a filter is clogged when fitted to the inlet side of an SU pump the pump will stall with the points closed and burn out the pump. If the filter is fitted on the outlet side of an SU pump the pump will stall with the points open (no current flow).


Mick
M F Anderson

With the aftermarket electronic pumps, they have no internal filter and will be destroyed easily by any junk in the fuel line. Therefore a filter before the pump is best. I use a filter before the pump and again before the carbs. I'm installing a new electronic SU pump which has its own filter screen, so I will now omit the filter between the tank and pump but will leave the one in the engine compartment.

Mark
Mark J Michalak

I know what the experts say, but I have a $2.11, G-2 plastic in-line filter on the “in-put” side of an SU pump. I put a new filter on every Spring. The old filters often look gross but they have never stopped the pump from working.
David werblow

Rick - The picture of your pump appears to be a Carter pump (they don't make a lot of noise like the continual chatter of the Facet pumps). 7.5 psi is way to high for the SU carbs. The OEM SU pumps for MGAs has an output pressure of 3.8 psi, which is approaching the maximum of 4 psi very closely and shouldn't be exceeded. You either need to get the low pressure version of the Carter pump, or install a pressure regulator (a new pump is probably the cheaper route).

It looks like my campaign to educate MG owners about external filters on the inlet side of SU fuel pumps has been successful considering the number of posts on this thread about not doing it.

David, your campaign changing out the filter every spring is the only thing saving your SU pump, but the fact that the filter is dirty each time says that you are treating the symptom rather than solving the problem of a deteriorating tank. This may work for a time, but could well back fire on you in out years. To reiterate, if the filter clogs to the point where it stops flow to the pump, the pump will stall in a current on condition and if power is left on for any period of time (such as when troubleshooting the problem) the internal swamping resistor in the pump will be burned out. This damage will not be apparent right away, but will instead cause the points to burn out prematurely. The really insidious part of this kind of damage is that new points installed to replace the burned out points will also burn out prematurely because the arc suppression circuit is defeated by the burned out swamping resistor. Further, if the pump is one of the newer all electronic SU pumps, the pump will stop working altogether and the circuit board will be severely damaged. Least people think that this is a rare problem, well over half of the pumps that I restore for people have damaged swamping resistors, ranging from minor overheating to completely burned out. Cheers - Dave
David DuBois

A couple of you have installed aftermarket fuel pumps, but indicate that you are changing back to the SU type. Reasons?

Thanks for the rapid feedback. My intent is to install a fresh aftermarket pump (Carter?) of known heritage, and drive at least this season with it. We will see what next season brings. My interests are not absolute originality, more biased toward trouble-free cruising.

Anyone in the Boston area going cruising on May 2nd?

Safety Fast!

Rick
rpb bunch

Rick - There is no compelling reason to use one brand of pump over the other. The only thing to watch with the after market pumps is that the output pressure doesn't exceed 4 psi (this not an issue with the SU pumps because they are all under 4 psi). All of the pumps on the market today are good pumps that will last somewhere around 100,000 miles. The only thing that the SU pumps have over the after market pump is originality (if that is your thing) and the only draw back to the SU pumps is that the points style ones do not take kindly to being left idle for long periods of time (this is not an issue with the all electronic style). Cheers - Dave
David DuBois

This thread was discussed between 11/04/2009 and 12/04/2009

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