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MG MGB Technical - Fuel filter puzzlement

Just helped my friend get his '71 running. It has HS carbs and a square after market (actually markets - he tried 3 different) fuel pump.

Has a good flow, can fill up a coffee can in a minute or so. Car runs fine, good power under load etc.

Fuel filter is a "universal" see-through design, and only because you can see the fuel does this question arise:

How much fuel should the filter have? Full, 1/2 or what.

At all times, his filter contains barely any fuel. At a glance you'd think it was empty. We even tried disconnecting the line from the carb and filling it up from a syringe. Started it and it emptied again.

Opened the float covers, and the bowls are about 2/3 full, which looked normal. Also removed the gas cap to insure there wasn't a vacuum in the tank.

My '74, with the same pump and filter, and HIF's is completely full at all times, which seems normal, considering the pump supplies fuel under pressure, and more has supply than the carbs can use.

This might be a "if it ain't broke don't fix it" situation, but it does have us puzzled.

Comments?

Phil Collura

For whatever reason, it's normal. My filter can be anywhere between nearly full and apparently empty and the car runs fine. You said your friend's car runs fine, so don't worry about it! ;-)
Rob Edwards

There was a similar post on either the B or midget section a couple of months ago. Lots of theories, but I don't remember anyone having a definitive answer. Seems like this is common on all clear fuel filters no matter what type of car they're installed on. I'm pretty certain that the metal can filters are the same, but like the light in the refrigerator, you'll never know for sure. ;-)
Bill Young

Sounds normal. Same think on my B with the plastic filter and on my VW with the glass filter. As long as it keeps running its good.
Luigi

Thanks all, until he had a running problems I'd never even looked at the filter so closely.

Our troubleshooting was over the phone until yesterday, when I made a trip to PA. So what got him running is a mystery. Just wanted to make sure I didn't miss something.

Phil
Philip Collura

Fitted one to the fuel line from the fuel trailer to my emergency generator. With gravity flow--it didn't even look like there was any fuel flow at all--empty---but last storm--it ran just fine that way. Must be some form of fluid dynamic magic or slight of hand. Maybe trap doors and mirrors.
R. L Carleen

Yes, cars can be strange :)
Mike MaGee

With my old SU pump, the reed valve (I think)
was letting fuel back into the tank and my
clear fuel filter often looked empty.

When I replaced with a new SU pump, it seems
that the fuel filter is now always full.
So maybe its just a function of how worn/effective
the fuel filter valve is.
Ronald

My V8 filter always looked empty except for a slight pulse as the fuel pump operated, so it wasn't a draining-back issue. Wasn't getting any running problems, but when this topic was raised some months back I disconnected and bled the filter till it was full, and it has stayed full over all these months and thousands of miles. If it runs just fine, ignore it.
Paul Hunt 2

This thread was discussed between 03/10/2005 and 06/10/2005

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