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MG MGB Technical - Fuel filter location

I fitted a fuel filter on my 71B, on which the flexible fuel line goes from the metal line into the back end of the carburettor supply, ie through quite a tight bend, rather than the round-the-houses route of later models.

The filter is the common plasic all-in-one type. It worries me that the tight bend and short hoses could strain the plastic nozzles on the filter and perhaps lead to fracture. This might cause me more grief than a fuel blockage. Any thoughts?

Tony
Tony Bridgewater

Tony-
fuel pumps and carburetors are precision instruments that do not take well to the presence of dirt. As such they should be well protected. Install a transparent fuel filter in the feed line just prior to the junction that feeds both carburetors, then install a second transparent fuel filter in the feed line that runs from the fuel tank to the fuel pump. If the transparent filters that you elect to use should happen to have glass housing bodies,
these can be easily protected by sliding a short section of transparent tubing over them. A petcock-type valve will simplify replacement in the future, preventing fuel from the carburetors from draining into the boot when the fuel line is disconnected from the filter. Whenever you see debris in this filter simply replace it with the one that is before the carburetors and then install the new filter in the line before the carburetors. By using this approach you can best protect the carburetors and the fuel pump as well.
Steve S.

Tony - As opposed to Steve S, I don not recommend a filter prior to the fuel pump. My reason for this is that any clog (such as a clogged filter) will cause the pump to stop pumping in a current on condition. If power is left turned on for any length of time with this condition existing, it will burn out the swamping resistor in the pump leading to accelerated point burning. In the case of the newer, all electronic pumps, it could lead to coslty damage to the circuit board (see my article on SU fuel pumps at http://www.custompistols.com/cars/articles/dd_su_fuel_pumps_101.htm)
I do agree with Steve's recommendation of shut off valves on the fuel lines. These will save you from a bath in fuel when having to change a pump or filter and can also serve as a cheap anti-theft device. Good luck - Dave
David DuBois

David and/or Steve, could you describe the petcock valve location and installation in more detail. I'm restoring a '72BGT.

Thanks!!

Tom
Tom Custer

Tom - I mounted the fuel shut off valve between the tank and the pump. The valve I used is a 1/4" ball valve and it can be fit to the fuel lines using 1/4" straight pipe fittings that can be obtained from Moss. A second valve can be placed between the pump and the carburetors if you want to completely isolate the pump. The easiest place to install this valve would be in the engine compartment.
Good luck - Dave
David DuBois

Thanks for the useful advice. Actually, my real poin was to ask whether it was mechanicaly sound to fit an in-line plastic filter in the v tight bend of the hose behind the carbs. I was concerned that the strain on the filter might cause it to fracture.

Tony
Tony Bridgewater

David

Where did you get your ball valve? Is is specifically for fuel service?

Thanks

Larry
Larry Hallanger

Tony

I fitted a plastic see through filter just before the final flex line into the carbs. I didn't do a good job first time such that pressure was put on the outlet pipe of the filter. After a few weeks this pressure on the outlet pipe caused distortion to the plastic housing at its base. The pipe didn't bend, the housing dented inwards. The pipe is at about 10 degrees from the vertical. If left any longer I am sure it would have ruptured. So the answer to your question is yes.

Richard
Richard Evans

Larry - I got it from either Lowes or Home Depot, but any large hardware store or industrial outlet will have them. The one I got is brass with a chromed steel ball in a teflon seat, so it works just fine with gas.
Cheers - Dave
David DuBois

Just curious...my plastic/clear fuel filter is at the rear of the valve cover and sits horizontal (parallel with the fuel line). The input port is horizontal as well as the output port. My question is: is it normal to see only half of the filter filled with fuel? I have never seen the filter full, so it looks like only half of the filter is being used. Maybe I have the wrong style filter? Thanks. -Rod
Rod in WA

Rod in WA,

Amen to that. Mine is located exactly as you describe. ( I put it there as there was none and did so after pump replacement with a SU instead of the aftermarket Bendix present) I got the clear filter from Moss Motors and have never seen it full. Also have never had any problem with fuel feed contamination, etc.etc.... after the SU, and new fuel tank

So don't think it matters if it isn't full. This is on my 66 B roadster/

Jim
Jim Hanks

If the fuel line enters and leaves the filter at the center of the filter and the filter is horizontal, the filter will always appear half full (half empty for pessimists).
This is normal and is the reason why all hydraulic cylinders have a bleeder valve at the top. The air cannot get out on its own. It does not affect the flow of fuel.
However only part of the filter surface is used. The solution is to rotate the filter occasionally or mount it vertically.

Mick
M F Anderson

new cars have hi pressure injectors which are very vulnerable to sediment in the fuel. These systems have filters that are generally a metal body and larger (holds more dirt). Some of them are easily adaptable with a section of neoprene hose on each end. I would choose one of these for under the car use.
Barry
Barry Parkinson

I can confirm the vulnerablity of fuel injected systems to sediment in fuel. I ran out of petrol a few months ago in my V8. When I put some more fuel in it wouldn't start anymore and both filters had to be replaced even though they had only done about 4000 miles at the time.
I decided to splash out on cleanable filters which I bought from Demon Tweeks. They are quite small capacity anodized aluminium cannisters containing a synthetic wadding material which has an extremely fine mesh. Very easy to remove the wadding periodically and rinse out the wadding in clean fuel. One is mounted close to the battery compartment between the tank and the pump. The other is mounted in the engine bay.
Marc

This thread was discussed between 27/06/2003 and 08/07/2003

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