I've still got a mystery air leak in my fuel system. The car has a greasecar kit on it, so it is plumbed in the following fashion:
on Diesel
diesel tank>spin on filter>valve>clear fliter>lift pump>IP>Return banjo (with solid bolt to separate from spin on filter)>valve>diesel tank
on WVO:
WVO tank (HIH)>WVO filter in water jacket>FPHE>valve>clear filter>lift pump>IP>return banjo>valve>looped back into supply between the HIH exit and the WVO filter with a T

The car runs fine on Diesel, but there is air getting into the line as I can see bursts of bubbles in the clear filter when I rev the engine. On WVO it runs fine (though a little lumpy at idle) untill it is put under high demand at which time it starts to lose power till I switch back to diesel.
I replaced the primer pump, which helped but did not solve the problem. I've replaced all lines and clamps. I've replaced all crush washers and o-rings. I even tried running clear lines so I could watch for the bubbles and that was inconclusive as to where the air was getting in. I picked up a fuel filter mount from the pull-a-part last weekend and the hollow bolt seems to fit in a bit tighter than the one on my car, so I'll swap that out and see if it helps.
Is it possible that the lift pump itself is sucking air in? Any other ideas?
thanks,
ben

i've been having a similar issue. my vacuum gauge is reading low when I switch over and the filter is virtually new, only about 10 gallons of fuel run through it so far. i've got a primer on the way, so i'm hoping the primer is just shot.

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1982 MB 300D-T
Veg Power Two tank conversion