MG Car Repair: Killing while driving, brake master cylinder, float chamber

Question
QUESTION: I recently reactivated a '76 MGB (US) that was stored for 10 years.  Did a whole mess of work, got it going, and started driving it.  After a few hundred miles, it's developed a problem that's stumping me.  While driving, it suddenly kills.  I can put it in neutral and start it, and it generally starts right up again, although sometimes it hesitates for a few seconds so I have to pull over to avoid getting rear-ended.  I can run it at any RPM forever in the garage, and it never happens.  But it now happens constantly while driving.
It has a Stromberg carb, recently rebuilt, and a 45D4 with a Pertronix conversion kit recently installed.
Suggestions on how to go about diagnosing this?

Thanks!

ANSWER: I think you will find that the fuel pump is starting to fail.  Under load, it cannot deliver enough fuel, the float chamber empties, and the engine dies.  Leave it for a few seconds, it fills up again and off you go.

Try cleaning the points inside the lid of the fuel pump.  I bet they are blackened.  They don't like being stored for years and then re-activated.

---------- FOLLOW-UP ----------

QUESTION: Thanks!  I wondered about that, then kinda forgot it.  The fuel pump is brand new, but it's not a standard MGB one at the trunk.  Instead, it's a Carter inline mounted just forward of the brake master cylinder.  Any familiarity with these, are they up to the job?  Could the heat of being under the hood be a significant factor?

Alternatively, might I get similar behavior if my float is out of adjustment?

Answer
No problem with the pump, but it is mounted in the wrong place.  Basically, these pumps are good at blowing but not very good at sucking.  The MGB SU pump is rear-mounted close to the tank and LOW DOWN so they don't have to suck too hard.  Also, a rear-mounted pump pressurises the fuel lines in the engine compartment, which makes them more resistant to heat soak, whereas a front-mounted pump sucks through the pipe, so the fuel in the pipe is under reduced pressure and more likely to vapourise.

I don't think the float is a problem.

/----------------- EXTRA -----------------/

I recommend Pertronix Igniters, I use them myself.  However, the 76 B has a ballast resistor hidden inside the wiring loom, and a ballasted coil so I hope the Pertronix unit was installed correctly.  An un-ballasted replacement coil must be fitted, and the power supply must be taken from a plain white wire, NOT the original white wire with the green stripe.