[Mgs] MGB driving me nuts

[Bernd]

alright folks, my 71 "B" is acting up on me, within the last month there have been three occasions where I'm driving along (say at about 60) suddenly I get a whiff of gasoline odor, then the car's RPM drops and the car starts surging. When I pull over to the side of the road the car idles at about 500 and tries to die out, I've checked the dampers in the cabs, the weird thing is when I press the dampers in the engines RPM speed up (should be revere se) I've checked the floats, I have Grosse jets and they are free, I've change to my good spare distributor  on the side of the road, after doing all those things the car starts to run fine again, then a few days or a week later it does it again, I'm stumped, any help?. should I look toward the fuel pump?
Bernie 
71 MGB