Very low pressure fuel pump

[binge]

Hey guys,

I've asked on a few mini-bike / pit bike specific forums already, and cant get much of an answer.

The Chaly will only use the first half of the tank.
Being gravity fed, once the fuel gets lower than that, it cuts out, both on reserve, and 'on'.

It seems to be a common thing with the Chaly and Dax.

I keep seeing vacuum operated pumps on ebay, but I cant help but thinks these are just fuel taps, not actual pumps.

It's just a single 26mm carb, so will literally need a couple of psi, if that.

Are there vacuum pumps available, as I'd prefer one of these.




Ben

[Teflon-Mike]

Small fuel pump from an old SU carburated car... if you have a 'head' of fuel pours straight through them, but if there's nothing in the 'out' line they cut in and start pumping. Search for electric fuel pump for Mini, or Morris Minor.
Later engines had mechanical pumps driven off the cam, but early ones had electric pumps, wonderful electro-mechanical things with points in them! After-market replacements had electronic controllers and were a nightmare when they burned out!
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[stinkwheel]

I do know an XTZ 750 fuel pump is vacuum operated because my mate fitted one to his transalp for use with an auxilliary fuel tank.

EDIT: Given the relative amounts of vacuum generated by the two engines, it's a fairly safe bet it'll be low pressure.

That said, why low pressure? The needle valve on a C90 carb is exactly the same as the one on a bigger bike and that's ultimately what cuts off the flow of fuel.
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[binge]

It's a Mikuni VM26 carb im running. Didnt think the needle valve would be up to cutting off a decent fuel pump?

Nice input Teflon-Mike, Will look at them.
So while there is gravity fed fuel, the pump will remain off?
But once it struggles to gravity feed through the pump, it'll kick in?


Ref the vac pumps. There are loads on ebay, but I'm not too sure if they are really just fuel taps. I remember my speedfight having a vac fuel tap.

And yeah, my thought exactly Stinkwheel, running a vac pump on my little 150 engine will be nice low pressure.
And with it being vacuum, if it's too high pressure, I'll just get a ball-valve, or an inline fish-tank valve to drop the pressure down a bit more.

[Matt578]

Something like Sucky Blowy Pump
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[hmmmnz]

most scooters have a vacume pump that would be suitable,
the honda dio we have has the tank below the carb, works a treat with the little stock pump
much like this one
https://www.ebay.co.uk/itm/Vacuum-fuel-pump-for-Chinese-125cc-150cc-250cc-Scooter-ATV-Jonway-Jmstar-Znen-/270922082086?pt=UK_Motorcycle_Parts&hash=item3f1436e726
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[Matt578]

That ones a beauty!
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[binge]

OKay, nice one guys. Will buy that last one.
I'm right in thinking I can simply drill my inlet manifold, then add a nipple into it, and run a piece of fuel pipe to this pump?

[Pete.]

[binge]

My setup is an alloy tubular inlet, with a push fit boot on the end of it.
But I dont think there is anywhere on the boot to go through, as the carb pushes right into the boot, and up against the flange.
Would probably just need to drill the inlet. Just dont want to ruin it as it's a good one (TB racing gas flowed jobby).




Ben

[binge]

Right, just bought a vacuum pump, hopefully it can draw enough fuel to overcome this starvation problem.
Speaking to DAX and Chaly owners, it seems a very common issue, especially when engine swaps, and elevated carbs are involved.
I'll probably mount the pump directly under the tank, and then run a long vacuum hose from the inlet, up to the pump.

Pete, I'll dig out an old manifold, and practice on it. Hopefully the alloy will be thick enough to drill and tap. Or is there a better way of doing it?