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MG MGB Technical - Fuel Starvation

First I just want to say thanks for all of the previous help I recvd thus far. This site is great!

My current issue is my 79 "B" seems to be starving for fuel. We have assured there is power to the fuel pump by going directly to the battery and that there is fuel delivery to the carb by disconnecting the supply tube at the Carb, which is a ZS 175. Is there a possibility that the fuel is being restricted within the carb from the fuel supply to the float?
The blockage does not seem to be between the pump and the intake at the carb. This seems to happen intermittently and the car will not start.








Elizabeth

It's not unheard of for a piece of dirt to block the needle valve in any carb. It's an accepted method to disconnect the fuel pump and run the carbs dry. Then reconnect the pump, turn the key on and hope that the rush of fuel through the valve will flush it clear.

It might be a good idea to remove the carb and open the float chamber. You can check the integrity of the float and needle valve, and see if you've got an accumulation of dirt.

Having said that, let me give an *opinion* that if it's intermittent, have a good hard look at the ignition system. Granted I've never owned a ZS, but the SU carbs are so simple that the problems they exhibit tend to be more consistent rather than intermittent. I hope that the same can be said for the ZS.

(I did have a two barrel downdraft Zenith on an air-cooled VW once, but that's another BBS.)



Matt Kulka

Because carbs have a float chamber it means it has a reservoir of fuel. Only under exceptional conditions would this empty while the car was switched off, which means that even if there is no supply of fuel from the pump when the engine is next started it should start and run for a while before emptying the float chamber and stopping. On a 4-cylinder car this could be a couple of hundred yards even when cold and using choke. Verify you have a spark at each plug and at the correct time when it next won't start before doing anymore with the carb "90% of carb problems are caused by Lucas electrics" quote unquote.

Does your Zenith have a automatic choke? Maybe that is sticking off. Sniff the plugs after cranking for a while when it won't start. A wet plug is flooded i.e. too much fuel. No fuel smell means no fuel in the cylinders, dry but a strong fuel smell is about right.
Paul Hunt

Well we found a twofold problem. Lack of 12 volts to the fuel pump and the fuel pump itself as we went straight to the battery for power. We bought a back up pump and went straight to the battery for power and we are now getting fuel. Lack of power seems to be in between the inertia switch and the pump.


Now onto the other problems - Ugh!

Elizabeth

This thread was discussed between 28/06/2003 and 30/06/2003

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