help! fuelling problems

[ewanhopkins@hotmail.com (Ewan Hopkins)]

Have had problem over the last week where, if I let the petrol level go 
below about 1/2 to 2/3 of a tank I get a misfire under load. Car has 
CIS-basic ( UK '85 8v) with bigger 55l tank, dual pump. Main pump doesn't 
sound any different from normal. Tank lifter pump is working, or at least is 
running. It's filter had a bit of crud on it but I let it dry out and 
brushed it off. Also changed fuel filter but no difference. Main fuel pump 
was changed 2 or 3 years ago. I'm guessing that the problem must either be: 
pump(s) are on the way out OR crud in the tank is blocking lifter. I haven't 
got round to taking the lifter out again to see if it has picked-up more 
crap. Have I missed any other obvious possibilities?
TIA,

Ewan Hopkins.

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