Ben came over today and was trying to use the fuel pump to pump out the
tank preparatory to getting it cleaned. Even without a filter could only
get a tiny stream. Tried a couple other fuel pumps. One ran but would not
pump anything, even blowing into the tank. The other one pumped a great stream,
even through a supposedly plugged filter. So I conclude that we have wiped out
a fuel pump. We'll put a cheap transparent filter between the tank and the
pump and see how that does. But I have a question:

What happens to a positive displacement pump so that it runs but doesn't
pump? I haven't torn them down yet but am wondering if the superfine
reddish brown rust might have worn them to where the clearances are too
great to put up any pressure. Maybe the soft end plates have gouges worn
(or polished) in them?

Let me know what you think and I'll let you know what I find out.
--
George Downs, Bartlesville, Oklahoma, Central US

I haven't opened one either, but sludge does seem to accumulate inside those pumps, at least, when I took mine off, a fair amount of brown stuff dribbled out. Since the pump had been working fine, I just flushed some clean gas through it. Yours may need a more venturesome approach.
Bob S.

Time permitting, I'll take it apart today and let you know what I find.
I will certainly mike both the diameter and length of the rollers and the
thickness of the plate.
--
George Downs, Bartlesville, Oklahoma, Central US

I have been told that it isn't such a good idea to put a filter between the tank and pump. Can cause cavitation and consequent 'iffy' pump performance. I guess that's why the standard filter is after the pump, not before it.
The pumps aren't really positive displacement types. They rely on centrifugal force to push the pump rollers out in their cage. Accumulations of crud and rust can cause rollers to get stuck in a 'non-pumping' position, hampering pump performance. The pump body should be held together with 4 machine screws. Easy job to pull it apart and clean everything. Check that the tiny drive pin which passes through the motor shaft is ok too.

Re: it not being such a good idea to have a filter between tank and pump.That could very well be right, but a plugged or destroyed in-tank strainer either lets through not enough fuel or too much dirt, neither of which helps the pump any. A clean see-through filter lets through plenty of fuel and, if you check it regularly, which is no great chore, is easy to replace when dirty.
Bob S.

George mentioned that he was thinking about fitting a filter between the tank and the pump. That's the filter I was referring to. Naturally a strainer in the tank which is in good condition is vital, not just to stop the ingress of muck into the pump, but it also helps in stopping water in the tank getting into the system too.