Moss Motors, Ltd

Ok, I have resisted asking for help (male ego thing) but I am at wits end. My 74.5 MGB with a Weber DGV carb will die intermittently going down the road. When it dies, I turn the ignition off (while still coasting down the road, car in gear), then turn it back on and it backfires (sometimes a little, sometimes A LOT), then takes off running. It might run for a 1/4 mile, it might run for 10 miles. It seems to be after it warms up and also worse on warmer days, although even this is not consistent. I have changed points and condensor. Plugs and wires seem to be good. I have done the check with the gas cap (listening for the "whoosh" when released) to make sure there is not a vacuum on the gas tank. I think it is running out of fuel. Any easy way to check fuel pressure while going sown the road? What should it be? Sorry for the long post, but I have tried many things and am out of ideas. Any help is greatly appreciated!!

When it "dies", does it suddenly expire, or slowly fade away over a few seconds?  If it suddenly quits, that would indicate an issue with the primary ignition circuit.  I'm not a "B" guy, but it seems many fellow posters have had issues with corroded contacts in the ignition key module.  A slow fade-away would point to a fuel supply issue.

It does cut out quickly. I forgot to mention that I did take the ingition switch out and sprayed with contact cleaner. Checking voltages (while sitting in the garage), all seemed well with the ignition swich. I was leaning toward an ignition problem at first, but then my mind switched to a possible fuel problem. Maybe I should check voltage to the coil while driving using some alligator clips. That would at least tell me up to the coil if the ignition circuit is ok. Thanks for the reply. Any other ideas are welcome!!

When you checked the contacts in the shop, they just happened to be working at that time! Monitoring the coil voltage is the thing to do here.

Also, is there a speed associated with this problem? If it works fine (when it works) at higher speeds, then it's probably not a fuel problem.

Another thing to realize, the carb may be prone to vapor lock if it is not properly heat shielded. I don't know if this is the case with you, but it is something to keep in mind since you indicate that the problem is more frequent when hot.

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

'68 Sprite 1275
'76 Midget 1500

What about  the fuel pump?  They seem to run a bit of a neglected existence, living where they do!! The symptoms sound just like I used to have on my YB [ however suck-pump near the engine rather than blow-one at the back, as on B] I used to keep a 3/8 ring-spanner handy and give the pump a couple of sharp raps to wake the points up when needed!

In the engine change, did the in-line fuel filter get omitted by any chance?  If its there what state is it in?? If not there, put one in. It could be fine crud in the fuel line  as well.

Cheers   steve

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To a man equipped with only a hammer, most problems look like nails

All... Thanks for all the replies! The problem is not speed sensitive. It mostly dies at highway speeds, but has also died at 25 mph in town and coming up the driveway (as I said "whew", made it home again!). Anyway, I think I will put some test leads on the coil to monitor the ignition while driving. If I lose the 12 volts going to the coil, then I at least know which direction to go. Girls have soccer tonight, so I am not sure when I will be able to try it out. I will post my findings here.

Thanks again :)