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MG MGB Technical - Engine cutting out, runs, cuts out

For a couple of weeks, my 70 B has been cutting out with a spitting,fluttering sound about every 15 minutes or so. Pull over and wait a minute, then it cranks fine and runs fine until another 15 minutes.

NOW, with temps at 28F this morning, I drove the B instead of the TD and it started cutting out every minute or two! Cranks right back up with a lot of ticking from the fuel pump and runs until the next 2 minute cycle.

Any ideas? Hope to be able to get home tonight but not sure what's up? Fuel pump?

Thanks in advance,
dave lackey

I would put money on the fuel pump, pumping but not keeping pressure, just sorted something very similar.
K Harris

Beginning to think it is indeed the fuel pump. Just went out to the parking lot, ran the car around the block and it cut out again. Brought it back and watched the fuel level in the transparent fuel filter whilst letting the car run. Seems the pump was pumping a pulse of gas into the filter every couple of seconds but then the level went down and could see no more pulses.

Should the pump be filling the filter continuously?
dave lackey

Yes because it should be under pressure.
K Harris

Dave - See my fuel delivery troubleshooting guide at:
Your problem sounds suspiciously like a fuel tank that isn't venting properly. Between the time you car was cutting out every 15 minutes and now when it is doing it every two minutes, did you fill the fuel tank? If so, I would definitely suspect a bad tank vent. Good luck - Dave
David DuBois

Dave, let's see...

The car was doing the 15 minute thing even on very low fuel. I put in about 6 gallons this morning and it was doing it every couple of minutes.

Just pulled the gas cap (on break...still working at the office) and looked at the inside of the cap. It has a spring loaded plunger for lack of a better description. It appeared almost flush (closed?) and I pressed on it with a pen. It clicked and I could see the spring action.

Blowing on the cap with the plunger closed, I can not get air to pass. If I push the plunger sideways and bind it up with the spring it remains open and allows air to pass.

Maybe I should just leave the cap with the open plunger? Not sure why it is spring-loaded unless it has to build up a certain amount of pressure to open the plunger like a valve.
dave lackey

Dave - I'm not sure about the 70 MGBs, the earlier ones (like our 66) had a vented gas cap, whereas our daughter's 73 had a tank vented through the charcoal canister, but I don't know where the changeover occured. If you car has a charcoal canister, then the tank is vented through that and not the filler cap. A tank that is not venting will cause the problem you are describing and it is worse when the tnk is full (less air space above the fuel). I finally figured it out on I5 in northern California on our MGB and drove the rest of the day with the filler cap in the passenger compartment. That evening in the motel room I cut a hole in the rubber gasket to get us home and got a new cap then. Good luck - Dave
David DuBois

The clue is in the 'cranks right back up with a lot of ticking from the fuel pump'. This implies that the float bowls had emptied i.e. the pump wasn't recharging them. It also indicates that probably the points themselves are at fault - probably spiked and sticking - as in some cases the shock of the pump solenoid moving back and fore just under the control of the ignition key can shock the points free - for a while.

Ignore the fuel filter. From mine and lots of others observations these can be anything from full to apparently empty, even on the same car at different times, and have no effect on running.

The vented cap should have a spring-loaded valve to prevent fuel leaking out in a roll-over. The valve will open when a certain amount of depression develops in the tank, which should be a lot less depression than will overwhelm the pump and stop fuel delivery. If I refuel my (UK) car when on a run I get a 'gasp' as I remove the filler cap because of this. Even if driving with the filler cap removed (only as a diagnostic of course) seems to cure the problem you still don't know whether it is being caused by a sticking filler cap valve or a weak pump. A replacement filler cap is cheaper and easier as a first step, but make sure it is a vented one.

Californian cars got the charcoal canister and hence the non-vented fuel filler cap for the 1970 model year, Federal and Canadian cars for the 71.
Paul Hunt 2

Did the same old stop/start/go...stop/start/go thing on the way home last evening. So, the gas cap did not seem to help!

Must be the fuel pump that I can pick up at Lamar's on

The good news? Whilst dining at the local pizza pub last night, my bride waxed lyrical about the B and how much she really enjoyed the comfort and heater when we toured so much in the past. She likes it so much (better than the TD), that she wants the B restored!!!!

The bad news? $$$$$$...ka ching. Yikes!
dave lackey

"comfort" and "heater" aren't usually words one hears associated with the MGB, unless the are preceeded with "lack of". But then it does depend on what one is used to :o)
Paul Hunt 2

This thread was discussed between 25/10/2006 and 27/10/2006

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