Anyone else have this problem?

My car has stiff suspension (cut down standard springs) with very little suspension travel. When it hits a big bump hard enough to shake the whole car it looses power for a split second then continues as if nothing happened. It's like someone gives the brakes a quick tap.

It also occasionally (about once a week) looses power completely. If it happens while I'm driving I put my foot flat to the floor and after about 10 seconds it clears itself and drives normally. If I put it out of gear so it's idling I can't get it to rev more than idle speed before it stalls. The only way to get the power back is to turn it off then back on and let the pump run for a few seconds before starting up.

Obviously it's a fuel problem but what's causing it?

Cheers

Paul