Adding fuel pump to gravity fed carb fuel system.

[KevTM]

ok i've got a wee project on the got and I want to do something different. The way it works just now is carbs with a gravity fed fuel supply. I'm going to need to use a fuel pump to pump fuel to the carbs.

How will it work or what will i need to do to make it work?

I'm just thinking forcing fuel into the carbs via a pump might lead to problems.. do I need to have a return from the carbs to the petrol tank? Do i need a way of turning the fuel pump off once the carbs are full?

My ZXR750 used carbs with a fuel pump so i know it's possible but just wondering if i'll run into any probs trying to pump a gravity fed system and how to rectify those problems..

Any info appreciated.

[mr jamez]

When the float bowl is full the fuel is cut off buy the needle valve. If you have too much pressure in the system the petrol will just keep on flowing. Quite a few bikes use fuel pumps on carbs, my BROS has one for example. I doubt any of these pumps are very powerful and I guess you could use them without a regulator.

My BROS hasn't got a return, I also retro-fitted a electric pump to my ford escort and that doesn't have a return. I think it is needed in a high pressure setup though.
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NSR 125F > BROS 400 > NC30 > BROS 400 > Trumpet S4 > '97 VFR 750

[KevTM]

Thanks for that! So long as I use a pump that isn't very powerful (Something from a wee 400 or something) I wont have to do anything spectacular? I Suppose running a regulator isn't much of a problem, never thought of that ..

[Pete.]

You can't use any old pump without a regulator. Many have them built-in but basically you need to keep fuel pressure down to about 2-4psi.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[finpos]

The type of pump you are looking for (i.e. one from carbed bike as opposed to FI) will just stop pumping when there is enough back pressure in the outlet. Either it'll have a regulator built in or it'll be diaphragm pump which will just stall.

f.

[Ichy]

FWIW the virago has a return system from the pump which feeds back to the tank. Don't know how it works but it primes the carbs then shuts down automatically when you turn the bike on. All seems to be built into the pump.
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[Pete.]

Many bikes run a prime when you put the ignition on, then stop until you crank the engine. The pump usually runs all the time the engine is running just that you can't hear it.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[KevTM]

thanks for the info guys, interesting stuff. basically all i need is a pump from a carbed bike, preferably a smaller cc bike... will give it a bash I'm pretty sure the ZXR never had any external regulators etc so may try find one of those.

[yen_powell]

You could just use a Mikuni vacuum pump. No electrics, just plumb it into the carb vacuum take off, or if you have a vacuum tap, off of that. KTM640s use them and I had one on my AT for a few years. They cost about 40 quid new, a company called Africa Queens was where I bought mine.
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Blackmail is a nasty word........but not as nasty as phlegm!
XT1200Z and a DR350 in bits

[Ichy]