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MG MGB Technical - Carbs dripping when engine off

I know there are some really good SU folks out there, so thought I would post this prior to fiddling.

I noted that when I turn my key on and the engine is not running, my carburettors leak. I understand that this is due to the fuel pump being on, but is there something I can do to prevent this?

There apparently is not a "accessory" position on the 67 B that allows the radio to be on and not the fuel pump. (I know, get rid of the radio).
BEC Cunha

I think my '67 does have an accessory position...turn the key to the left.

It doesn't alter the fact that either your float valves are worn, or your fuel pump has too much pressure.
Dave O'Neill 2

Or a float is sunk or partially so.

Could be just a momentary bit of dirt trapped in a valve, so electrically disconnect the fuel pump and run the engine till it conks out i.e. float chambers empty. Then reconnect the fuel pump, and the resulting rush of fuel through the now wide-open float valves (normally they are only open a fraction except after being switched off for some time, and then only open a little) can often clear a speck of debris. If that works and it doesn't come back all well and good. If it comes back after a while then maybe the fuel is dirty from a corroding tank, adding a fuel filter may help. If it leaks again straight away change check the float, and if that is OK change the valve.

Quite easy to deal with floats and valves on HSs (which I assume yours has being a 67) just by unscrewing the lid. If it is the opaque brass float you will have to remove it and shake it by your ear to hear the fuel. With translucent plastic it should be visible with a light behind it and shaking it.

Paul Hunt 2

As Paul sugests about the floats-- When you say "dripping" what comes to me is that the bowls are over filled because the floats are allowing too much fuel in -- or, inother words, the floats are not shuting off the amount of fuel into the bowls.

As stated above, the adjustment for the floats is very simple, but you'll need some kind of shop manual for the basic details -- (ha! - basic details).

Do you have the piece of rubber tubing that directs this over-flow down away from the exsaust manifold? -- or does your dripping flow out into the engine bay area.

just some idle thoughts.

It's generally a bad idea to sit with the key in the "run" position without the engine running -- if you have points and they happen to be closed, they can burn or you can overheat the coil. If you have a pertronix Ignitor, Pertronix warn to limit the time with key on/engine not running to less than 2 minutes.

That said, the real issue still needs to be addressed or your fuel mixture will be off...
Rob Edwards

Thanks all. WIll check the floats and the seats. Does anyone else have an accessory spot on their MK1 ? I tried going to the left and there is nothing there that I can tell.

I have always been careful about leaving the key on without the engine running. I was always told it was bad for the coil. I also have the petronic so that is another good reason.
BEC Cunha

Accessories position didn't arrive until 69 model year, and it was always the first position in the 'normal' direction, with ignition being second and crank 3rd. You could wire the radio to the purple circuit (fused but always on), and remember to switch off. Or you could wire a switch in series with the coil and turn that *off* when you wanted to listen to the radio. If you connect it in the appropriate place you can shut off the pump as well as the coil, but from what I can see this would have to be right at the switch, all except the radio feed. This would also act as an immobiliser.

I had occasion to change the coil, and almost immediately left it switched on for 15 minutes or so. I was rather annoyed to find the car wouldn't start immediately afterwards, but when the coil had cooled down (it gets very hot when the engine isn't running, much more so than when it is) thankfully it was fine. Can't remember that happeing with the original coil, and I'm sure I would have left that on at some point as well. Maybe the new coil has some kind of thermal protection.
Paul Hunt 2

This thread was discussed between 02/07/2007 and 03/07/2007

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