Fuel filter partial vacuum?

[vincereynard]

I have just fitted a Huco "sucker" pump and it is not delivering anything like the flow it is specified
to acheive. I'm going to bench test it pumping between containers with new 8mm hose on both sides.

A possible / potential problem I have noticed. I had 6mm to the filter and 8mm filter to pump.
Naturally the 6mm cannot keep up with the 8mm and the filter empties!
Therefore it would have a partial vacuum inside the filter?

Options ??.
1/ Drop filter so it is below pump (The +2's high mounted tank -
little help from gravity except with a full tank.)

2/ Run 6mm also from filter to pump. (However the nylon is 6mm external,
the rubber 6mm internal, so the pipe from the tank would still be a
partial restriction.)

3/ Mount filter after the pump so the fuel is being pushed through it.

An suggestions?

[2cams70]

Check the tank or fuel cap venting. Take the fuel tank cap off on a temporary basis, try again and see if things improve.

[alan.barker]

If you still have the original very big breathers on a +2 i would not think it is lack of tank venting.
I always keep the filter between tank outlet and pump. This keeps the pump clean.
Imho you need the same dia through all the length of the fuel line upto inlet on carbs.
Have you tried to see if car runs without measuring flow rates
I'm sure the Huco flow rate is still more than the old ac delco mechanical pump.
Alan

[Craven]

In a practical situation the pump will not be delivering fuel at its rated output, therefore your test setup is not really relevant.
As the total carb input is 2x 1.75mm then test with an output restriction of say 4mm.

Edit Sorry Typo

[vincereynard]

In a practical situation the pump will not be delivering fuel at its rated output, therefore your test setup is not really relevant.
As the total carb input is 2x 1.75mm then test with an output restriction of say 4mm.

The test was mainly to establish if there was a fault with the pump.

With an 8mm inlet and 6mm outlet it pumped 3.3 litres in 2 minutes. Reversing the pipes made very little difference. Blowing through the filters offered no real resistance.

Yet connecting the pump to the filter outlet only pumped a meagre 250 > 300 ml a minute.
Logically the feed pipe must be offering serious restriction of some sort??

Is a 6mm (external) nylon pipe the usual feed from tank to pump? The internal diameter is about 4mm.

[pharriso]

Is a 6mm (external) nylon pipe the usual feed from tank to pump? The internal diameter is about 4mm.

Original nylon pipe is 1/4" (6.35mm) OD

[alan.barker]

I would think that's more than twice the amount of fuel the car needs.
Sorry but have you tried driving the car yet.
Please take it for a test drive

[vincereynard]

I would think that's more than twice the amount of fuel the car needs.
Sorry but have you tried driving the car yet.
Please take it for a test drive

The last 3 times I did that it did not end well!

80mph at 20 mpg (?) = 4 gallons per hour.
30ml X 60 = 18litres = 4 gallons

Sounds marginal to me or are my maths rubbish?

[nmauduit]

With an 8mm inlet and 6mm outlet it pumped 3.3 litres in 2 minutes. Reversing the pipes made very little difference. Blowing through the filters offered no real resistance.

Yet connecting the pump to the filter outlet only pumped a meagre 250 > 300 ml a minute.
Logically the feed pipe must be offering serious restriction of some sort??

Is a 6mm (external) nylon pipe the usual feed from tank to pump? The internal diameter is about 4mm.

3.3l/2min gives about 30gallon/hour, which should me more than enough for a 200+ HP engine : since issue only arises with the filter before the pump, it could be that the filter is already clogged ... or that it prevents the pump suction for normal operation. I doubt that some air/vacuum build up within the filter would have any effect, but you should easily see that with longer hoses allowing the take the filter further down for test purposes.

then checking filtering particle diameter : you may want a coarser pre-pump filter and a finer post pump filter if indeed your pump can push but has a hard time to pull.

[alan.barker]

I thought 70 mph in UK was max on motorways
Maybe a bigger/larger filter would restrict less.
Alan

[vincereynard]

Tank fuel pipe connection blocked by insulation. That cannot have helped!

Perhaps it was floating in the fuel until I drained the tank? Then got sucked into the union and
lurked there just waiting. How it got into a new sparkly tank is a mystery.

I'll flush the tank out with a couple of gallons just in case.

[alan.barker]

Looks like machining swarf to me
Good job you put the filter before the nice new Huco
I must admit the outlet at the very bottom of the tank on a +2 is not a very clever design + it's a pain in the neck to access .
Well done Vince you'll get there in the end. Can you see the light at the end of the tunnel
Alan

[vincereynard]

I must admit the outlet at the very bottom of the tank on a +2 is not a very clever design + it's a pain in the neck to access .
Well done Vince you'll get there in the end. Can you see the light at the end of the tunnel
Alan

Not very clever design is one way of putting it! Design by whatever is cheapest I imagine.

P.S. With the rubbish removed the Huco now pumps a steady 1.1 litres a minute from the carb. joint pipe.
So that OK .