how can i fix a lucas injector pump?

i have a lucas injector pump....i tested the pumps cc's output on my pump tester....its up around 75cc's (perfect)
when i put the pump on the track machine it starts rapidly but then cuts out after 10 seconds or that? its like the booster mechanism activates and cuts out the engine? any help? i think its the length of the booster pin thats the problem? i can measure this one and its 37.5mm i cant find the old pin so this is the only thing that could be wrong with it? ive checked it over and over....at first i thought it was the meter valve but replaced that and it works on my testing machine grand but not in the track machine?