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MG MGB Technical - 74 MGB Fuel line and Pump
I have a 74 MGB. This winter has been a tough one for both the car and me as I have had to travel and when I was home the weather wasn't conducive to driving. Haven't started the car in 5 months (under cover, but not stored indoors). When I reconnected the battery and went to start her, I didin't hear the familar 'click-click" of the fuel pump moving fuel to the motor. Of course, the car didn't start (turned over, no start). Note that the fuel filter (glass capsule) is dry as a bone. Couple of questions: 1) will the fuel pump work if the line itself is blocked (should the first step be to check for line blockage?)2) does the gas pan in the carb (HIF Dual Carb)have a sensor to tell the pump that gas is needed and this could be the source of the problem? Are there steps I should go through to trouble shoot that you have found successful?
Thanks for any help!
|JUST GIVE THE PUMP A GENTLE TAP WITH THE IGNITION SWITCHED ON. THE POINTS COMMONLY STICK AND WILL USUALLY RESTART WITH A TAP. MOST UNUSUAL FOR PIPE TO BLOCK WHEN CAR IS NOT IN USE. CARBS ARE NOT FITTED WITH A SENSOR THE PUMP CUTS WHEN THE NEEDLE VALVE IN CARB CLOSES AND CREATES BACK PRESSURE. HAVE YOU CHECKED THAT ELECTRICAL FEED TO PUMP IS GOOD, SOMETIMES CORROSION ON TERMINALS OCCURS WHEN CARS ARE STOOD FOR LONG PERIODS ? JIM|
|If Jim's solution doesn't remedy the situation, you will have to remove the fuel pump and clean, or replace, the points. Now would be a good time to send it to Dave Dubois to have it rebuilt and converted to an all electronic unit to eliminate this problem in the future. RAY|
|Check the fuel filter. Last year I broke down, couldn't hear the pump clicking, convinced the AA guy it was the fuel pump, and got him to tow me home. |
Took the fuel pump off, bench tested it, nothing wrong.
The fuel filter looked OK, but a new one cured it.
|To JEs questions:|
If the line from the pump to the carbs is blocked the pump will only click once every thirty seconds or less frequently.
If the line from the tank to the pump is blocked it should click more frequently than that.
All MGB carbs have a float and a float valve, and that is the 'sensor'. When fuel is needed the float drops, opens the float valve, allowing pressure from the pump to push fuel through. It's possible the float valves have stuck closed, although this is unlikely as the fuel level in the float chambers would normally drop a little very soon after switching off, and hence open the valves, which is why we get the rapid clicks from the pump when we first turn on the ignition.
What's in a fuel filter isn't a reliable indication of anything, it can be anything from almost completely empty to full under normal running conditions.
It is quite likely to be the pump points oxydised, although five months isn't long, new pumps comes with a slip of paper saying to clean the points rather than return the pump as they can even oxydise in the box. Tapping the pump might help, but you might have to remove the end cap and use a thin file or just bridge and unbridge them with a screwdriver to cause the pump to operate and release until they have cleaned themselves. This not too bad if you have a rubber bumper, awkward with a chrome, so before you start opening up the pump check you have 12v and earth right at the pump terminals before you start opening it up. It would be annoyimng to spend hours fiddling with the pump only to find it was something else much more simple.
|Paul Hunt 2010|
|Thanks to all. I did check the connection, getting 12v to the device when testing. Still no sounds (no clicks at all). I undid the fuel lines to the pump and tried it while the line's were unhooked, no clicks. Gentle taps didn't help, but maybe I'll try that again. Figured I just need to suck it up (no pun intended) and order a new one or send it to Mr. Dubois. May clean the points if I can get the time. |
Again, thanks for the help and the information. Everytime something like this comes up I learn about the girl one piece at a time!
|If you are going to take it off to send it away or fit new then open up the electrical end first and poke at the points while you have a couple of jumper wires from the purple fuse and earth. You will feel so proud of yourself when it bursts back into life. Remember even a new one may need this treatment before it will work!|
|Paul Hunt 2010|
This thread was discussed between 01/04/2010 and 05/04/2010
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