90 fuel starvation

Can anyone suggest a solution to a problem I have with my 90. It starts- it runs but once you get past 35 -40mph it dies on you - feels like fuel starvation as if you wait a few seconds it starts again no problem. It has teh standard weber carb but someone (previous owner) has fitted a Facet petrol pump and done away with the filter.
It looks as though the old pump is still in place in the tank (they do come with the pump in the tank originally don't they?)
If it had a filter I would check that - any ideas?

fuel pump sounds like its on its way out, otherwise could be yer fuel pressure regulator or clogged filter at the fuel inlet to the carb. definately put a filter back in yer supply line!!!!

Thanks for the advice - I have checked the carb it was clean. The pump clicks away madly all the time so I guess it needs replacing as it is a replacement to original I assumed it would be OK. It is driving me mad!