MG Car Repair: 1976 MGB dies under load, vacuum gauge, fuel pump filter

Question
My 1976 MGB starts fine, idles fine, revs fine.  It has progressed to the point where when I drive it under load it acts like it is starving for fuel after quarter mile.  I struggle to keep it running by pumping the gas.  After I turn it off for a minute it cranks and runs normal for 30+ feet and cuts out again.  Replaced fuel pump, filter, no h20 in fuel. Changed coil, condensor, points.  Any thoughts ?

Answer
Hi Wally,
It is expensive to find a problem by replacing parts until you happened to hit what is wrong. The best way is to run a few tests.
First put a manifold vacuum gauge on the intake and run the hose out from under the hood and put the gauge under a wiper arm so you can read the gauge when driving. Read the gauge while the engine is still turning and has "Cut out" and let me know what the gauge reads.
A vacuum gauge is not expensive nor a few feet of extra hose.
Let me know,
Howard