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MG MGB Technical - Regarding fuel filters

Hi all.

I usually live on the midget boards, but we've had a topic running for a few days now that applies to Bs as well, and I'd love to hear some additional opinions.

Why is it that when you use clear fuel filters, they usually appear only partly full... and sometimes look near-empty, but the car continues to run fine? I have a filter right at the carb, and you'd think that the (mechanical) fuel pump would keep the thing full; and even though it starts off full, once the car has run a bit, the fuel level drops until it looks nearly empty.

Is that fuel vapor in there? Air from somewhere in the system? my fuel lines are new, so there shouldn't be any air being drawn in. And why isn't that vapor pumped through into the float chamber and vented?

Thanks for any ideas. I noticed this the other day and thought it looked really abnormal, but numerous Midget owners have reported in, saying "they all do that, don't worry." So I just want to see what you "B" guys think.

-:G:-
Gryf Ketcherside

I've got one on my VW and it also does that. Don't know why.
Luigi

I fitted a new filter to my B last weekend and it is only a little over half full. The old one was the same and I put it down to being air that gets trapped as it is above the inlet and outlet. I have never had fuel starvation problems so "if it aint broke, don't try to fix it"

Maurice
M Irwin

As fuel in the tank sloshes around, the fuel pickup tube may get exposed to air, and I suppose the fuel itself may get a little aerated on a bumpy road. Anyway, as this air flows through the fuel system, it gets trapped in the filter because the filter outlet is not at the highest point of the filter.

It's really not a problem because if there's enough air bubble in the filter to reach down to the outlet, it'll get pumped out to the float bowl and escape out the vent. Since you're always pushing mostly fuel into the filter, that's what'll get mostly pushed out to the float bowl as well. When air gets into the line which goes to the float bowl, it's no big deal because the pump has enough capacity to push a little air and still enough fuel to feed the motor.

If you turn your filter so that the outlet is at the very highest point, the air will make its way out. But if any of your friends see it, they'll probably think you're getting a bit obsessive and may organize an intervention.

FWIW.
Matt Kulka

Possibly because when the outlet of the outlet is at the top (which mine is) its inlet is at the bottom. The filter on my V8 looked almost completely empty at one point, which bothered me somewhat, although it ran just fine. Nevertheless I bled it, checked it some time later, and it was still nearly full. Could well be air bubbles from the pump etc. getting trapped in it because of the position of the ports internally, but makes no difference anyway because as soon as any air reaches the float chamber the float valve will remain open and the pump will continue to pump until the fuel level *does* rise to shut off the supply. Doesn't quite explain why bleeding it removed the air but driving didn't, but there is is.

JFDI.
Paul Hunt

This thread was discussed between 21/04/2005 and 22/04/2005

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