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MG MGB Technical - Sputters and quits

New rebuilt engine over a year ago with less than 1000 miles on the car since rebuild. For the first few months everything was great and then, after about five to ten minutes the engine now sputters and dies. Interestingly, after about 30 to 45 minutes it is ready to go again for another 30 to 45 minutes. Could it be the coil, or does anyone have any suggestions???
James Headley

Bad condenser in the distributor?
Could also be the coil, or any number of connections in the LT circuit.
Jeff Schlemmer

Something in the fuel tank? When it's not running (no suction), it floats away?
Tom

Another possible is fuel starvation. What year B do you have and have you made any modifications to the fuel system?

From 1966 up until about 1988 I had always driven CB models with twin SU's. In '88 I bought a well used '76 to refurbish for my oldest daughter. It was fitted with a bunch of extra crap in the engine bay that I didn't understand and I couldn't get it to run properly. So, I started taking things off the engine and eventually ended with a motor that was configured much like my beloved '66. The thing started easily and ran quite well for a few mile or so - then it sputtered and quit.

Couldn't get it to start and I had no tools. Walked to a station, called my wife and told her to bring the tow bar and my tool box. She picked me up and we drove back to the B. On a whim, tried to crank it one more time. Bugger started right up after about 15 seconds of fuel pump clicking. Told my wife to follow and headed for home. Got about a half mile from home and the thing quit again. Checked the fuel bowls and they were empty. Banging on the fuel pump - didn't help. Hooked it up and towed it home. Later, after a couple beers, went out to the driveway prepared to pull the fuel pump or something.

Being curious, turned the key one more time. You can guess - heard some clicking, waited for it to stop, hit the starter and it roared to life. Figured it had to be the contacts in the fuel pump. So, pulled the pump and bench tested it. It seemed to function fine, but popped the cap anyway and cleaned the contacts. Reinstalled the pump, but waited another day before taking it back out on the road. Probably had had four more beers before I got the pump back in the car.

Took it out again the next day with the tow bar and my wife giving chase. Not sure how far I got, but it quit again - no fuel. Following the same script, towed it home, parked it in the driveway, drank two beers, turned the key, clicking and it started right up.

Began thinking a case of beer in the passenger seat might keep it running, but my wife said - NO WAY. Tried a number things over the next couple of days or so, to no avail. Just seemed to run fine in the driveway. Then, having run the tank to near empty, I loosened the gas cap to add some fuel. I heard a distinct sucking sound - like when you open a new jar of dills. My gas tank had been under vacuum - but why?

Well - because I had sealed the system and it couldn't breath. When I got the car, there was a strong smell of gasoline in the trunk. On inspection, I found the rubber hose from a nipple on the fuel tank to the vapor separator (mounted inside the right rear fender) was broken. So, I cut the line close to the fuel tank and plugged it with a short metal rod. What I didn't realize, at the time, was this line allows the fuel tank to maintain atmospheric equilibrium as fuel is pumped to the carbs. After some head scratching and another beer, I fitted a new piece of hose from tank nipple to vapor separator. Reminding my wife again of my brilliance, I asked her to follow with tool box and tow bar in hand.

Problem solved - my daughter drove this B for the next six years, followed by my oldest son for another four.


P.S.
Another possible problem site is your ignition switch. Sometimes, old and worn, these switches will lose or cut the necessary 12V to the white lead that powers your fuel pump. When your car dies the next time, leave your ignition key as is and check the voltage at the fuel pump. I once had to rig a secondary 12 volt feed from my tail light to the fuel pump in my '80 LE. Eventually replaced the ignition switch, but as a temporary fix, I would turn on the lights to keep running.


Steve Buchina

James - See my fuel delivery troubleshooting guide at: http://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
Good luck - Dave
David DuBois

First test on a non-runner is to clip a timing light (inductive pickup) onto the coil lead and each plug lead and watch the flashes as you crank. No flashes on any lead is probably ignition LT or possibly a bad coil. Flashes on the coil lead but not plug leads is probably rotor or cap breaking down. Flashes on all of them, if a new set of plugs makes no difference, is probably fuel. If you get this far take a fuel feed pipe off a carb and direct it into a container, with the ignition on it should deliver *at least* 1 Imperial pint per minute.

If no timing light flashes on any lead check the ignition LT with a volt-meter or test-lamp - at least if you have points or the 45DE4 (integral amplifier) distributor, 45DM4 (remote amplifier) and aftermarket units can be very difficult to diagnose short of substitution. With points or 45DE4 you should have 12v on the coil +ve or SW at all times on a chrome bumper, and on a rubber bumper 12v when the points are open and about 6v when they are closed. With both chrome and rubber on the coil -ve or SW you should have 0v (ground) when the points are closed and 12v when they are open. With the distributor cap off flicking the points open and closed (ignition on) should generate a good spark from the coil lead to the block of at least 1/4". If it barely jumps a plug gap, and there is a lot of sparking and spitting from the points, the condenser has failed.
Paul Hunt 2

This thread was discussed between 19/06/2006 and 20/06/2006

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