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MG TD TF 1500 - fuel leak

I haven't spent any effort diagnosing this yet but I wanted to throw it out to see if anyone has any ideas. I have about 1000 trouble free miles on my TF since rebuilding the carbs and installing a new fuel pump. It is an early sn 0669 so the fuel pump is on the fire wall, All of a sudden, I am getting fuel overflowing both carb bowls particularly when the engine isn't running but the key is on but I even had quite a fuel puddle develop just sitting with the key off. Almost as if the fuel was siphoning. It sure seems as if both float valves are not sealing. weird that it would happen to both at once. The tank underwent a cleaning and sealing effort last summer. I sure hope it isn't shedding sealer. Is there any possibility the fuel pump is overpressurizing? Anybody else ever had this happen? I will probably be smarter when I take things apart.
bew wright

So it is coming out of the overflow pipes...not any of the connections?
gblawson(gordon- TD27667)

If the car has been sitting for awhile, a good possibility is that both float valves are sticking.
This is occurring due to residue from the fuel, especially fuel with ethanol added.

Remove the float chamber tops and clean the valves with spray carb cleaner.
I do this by disconnecting the fuel hose from the pump, and removing both covers and the connected hoses as an assembly. This saves having to undo the troublesome banjo bolt fittings. Sometimes the float valves can be sprayed while still in the cahmber cover, but I usually remove them from the cover to clean.

If you have the float valves with the balls, the small inner ball will sometimes seize in its seat, and the valve will need to be soaked in cleaner. I then just unscrew the valve from the cover and soak it in a small amount of cleaner sprayed in the cap from the spray container.

Be aware of and keep up with the small gaskets under the valves, and return the valves to the same covers. These gaskets also serve as adjustments to the float chamber level.
Dallas Congleton

But why "I even had quite a fuel puddle develop just sitting with the key off." ??? Is it really siphoning??


Remaining pressure in the fuel system, and/or expansion.
Dallas Congleton

What's the ambient temperatures, if it's in the high 80's and after a run the engine compartment will be very warm and therefore a certain amount of expansion of the fuel can be expected, but there shouldn't be enough to cause "puddling" just an overpowering smell of fuel.
Mick 52TD
Mick Cook

" installing a new fuel pump" and "Is there any possibility the fuel pump is over pressurizing?

What type of fuel pump was installed ?
Dallas Congleton

I vote for sticking float valves. You could also have a stuck or flooded float, but it seems unlikely that both would sink at the same time.

An easy way to see if they are sticking is to get the carbs to overflow with the key on and tap the float chambers with a screwdriver handle. That's usually enough to dislodge whatever is causing the valves to stick, and the fuel flow will stop.

t lange

Dallas has a valid point about the fuel pump, but only if it is not a SU pump. It is absolutely impossible for a SU pump to put out excessive pressure. I would go for the flooded float, stuck needle valve or even the needle valve jamming between the float lever and the valve seat, creating a situation where the valve is open but the float is unable to raise with the fuel level. This latter situation only occurs after the fuel has evaporated out of the float bowl, allowing the float lever to drop below a critical point, where the needle can stop it from rising with the float. For information on this situation and how to cure it, see the article, Float Lever Drop Adjustment in the other Tech Articles section of my web site at: Cheers - Dave
David DuBois

Off the subject a little but Dave, thanks for the fuel pump last year. Works like a charm.
Tom Maine (TD8105)

I apologize for being out of touch while so many of you were asking me questions. The fuel pump is a new su pump. One carb is leaking profusely through the overflow. The other was leaking thru the plunger device on the top. I like the theory that the leaking with everything electrical off was from expansion. The car was fully warmed up on a warm day. I am going to service both float valves and I am going to make sure both floats are not taking on fuel. To the theories relating to the car sitting, there might be something to that. The car has not run the first tank of fuel through it since 7 month storage. I can't help it. I live in Vermont and we don't see the ground 6 months of the year. Thank you kindly for all of your thoughts.
bew wright

Make sure the floats are not stuck to the bottom with the Ethanol junk.
George Butz

I had some time to look in to the float valve problem yesterday so I will report. First, I confirmed the fuel pump I installed was correct for early TF (firewall mount). It was the correct pump according to Moss and the box says 1.5 PSI. After taking the car on a run and getting it up to speed and temperature, the fuel pump will overflow the carb reservoirs with the engine off and the key on. I changed the float seats and needles back to the original type (the rebuild kit came with a fancy plastic needle with a spring loaded mechanism). Really, that didn't make much difference. I notice that the pump cycles about every 15 seconds when I turn the switch on cold. I was able to confirm that this is not leaking past the float valve so when the engine is relatively cool the float valves are effectively holding back against the fuel pump pressure and the cycling of the fuel pump must be related to pressure leakage at the pump (I was able to observe This by removing both reservoir tops and holding the valves shut manually. I had no observable leakage but the pump continued tho cycle 4 or 5 times a minute). Different story when things are hot. I think the expansion or potential boiling of fuel in the carb reservoirs and fuel lines increases the pressure and upsets the float needles. I don't have any other explanation. It would seem if I am correct, others would have experienced the same. So, I have had a puddle of 8 inch diameter under the carb overflows after parking the car hot but certainly not every time. Similar experiences anyone? The float arms are correctly adjusted.
bew wright

This thread was discussed between 28/07/2011 and 02/08/2011

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