carb fuel pump

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nick9one1

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posted on 2/8/18 at 02:52 PM

carb fuel pump

I've wired my fuel pump to the switched 12v, so it constantly powered while the engine is on.

Is this correct? - I've just read that the pump only primes when cranking?

My tank is about level with the engine, so how would the fuel continue to flow once you stop cranking?

Davedew

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posted on 2/8/18 at 03:07 PM

What type of carbs & fuel pump have you got?

Bike carb fuel pumps self regulate and turn on and off as needed.

Normal lower pressure fuel pumps normally need a fuel pressure regulator and possibly a return to the tank, so would be running all the time.

Posting Freak

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posted on 2/8/18 at 03:50 PM

As Dave says, when running bike carbs the pump runs until the floats fill and close the float valves.

When there is nowhere else for fuel to go, pressure builds up and the pump automatically stops, kicking back in as needed when the float level falls.

The pump must have a supply when the engine is running in a normal bike carb installation otherwise there would be no fuel once the floats empty.

nick9one1

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posted on 2/8/18 at 05:44 PM

Thanks I thought that was the case.

I've just using a cheap zzr1100 pattern pump from eBay. Engine is zzr1100.

Engine runs, but pump is quite noisy. When the carbs are empty the pump 'ticks' quite loud, getting slower as they fill.

You can hear it start at about 19 seconds, getting slower until the engine noise drowns it out.

[Edited on 2/8/18 by nick9one1]

Davedew

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posted on 2/8/18 at 06:35 PM

Does sound loud, but the way it is working is normal.
If you watch the video when engine is running something is dripping from under it. Just incase you weren't aware.

nick9one1

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posted on 2/8/18 at 07:53 PM

quote:
Originally posted by Davedew
Does sound loud, but the way it is working is normal.
If you watch the video when engine is running something is dripping from under it. Just incase you weren't aware.

You have sharp eyes! Thanks!

There's a oil line that seems to be steel and has rusted though. I've just ordered some parts to replace it.

nick9one1

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posted on 5/8/18 at 04:38 PM

I think I misunderstood what I previously read about the fuel pump.

It seems like a lot of bikes don't prime before the bike is started. So with the key at ignition, the pump won't be functioning, but once you hit start, the fuel pump kicks in and continues to run until the bike is turned off.

Davedew

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posted on 5/8/18 at 06:02 PM

With mine as soon as I turn the ignition on, if the carb float bowls are low the pump will run and fill them with fuel until pressure builds up.

Been like this ever since I built it in 2014 with no problems 👍

nick9one1

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posted on 5/8/18 at 06:12 PM

Thanks - Yep I'm sure youre right, there's no reason it should harm anything to prime before start (like a car).

I guess because bikes have shorter fuel lines, and the tank is above the engine, the carbs and lines will stay full. So it's unlikely to need a longer prime.

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