Fuel pump not priming

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Re: Fuel pump not priming

Post by Suzuki416 » Tue Jun 11, 2019 8:12 am

xstian wrote:
Mon Jun 10, 2019 5:26 pm
Hi thanks for the reply.

I believe understand how the relay works, although there does seem to be a few different ideas on it.

When the bike gets low on fuel, the carb float bowls empty and the bike starts to conk out. Turn the petcock to reserve and the pump fills the float bowls back up and you carry on, usually with out the need to stop. So the pump should be capable of filling the carbs when the engine is running or the starter is engaged, without the need to bypass the relay.
xstian wrote:
Mon Jun 10, 2019 5:26 pm
I don't believe the relay has any influence on the pump, other than to feed it power when the engine is running or the starter is engaged.
Yep that's correct - It is more down to the design of the pump doesn't like sucking air.
xstian wrote:
Mon Jun 10, 2019 5:26 pm
I've also replaced the contacts in the pump. Also is the tube coming off the plastic cover just a drain?
Its a drain
xstian wrote:
Mon Jun 10, 2019 5:26 pm
Thanks for taking the time to reply.

If you have to bypass the relay to make the pump run continuous, that's would mean the relay only give power to the pump in short spurts to top up the float bowls. I'll try and test this with a multimeter this afternoon.
DO NOT BYPASS THE RELAY OTHER THAN TO PRIME THE PUMP.. The design of the pump means it is a bugger to prime when its not got any fuel in. There is no other purpose of the bypass wire than to prime the pump. It is NOT to be done to keep the pump running - just put it on for 3 or 4 seconds & you will here the ticking almost cease. At that time disconnect the Bypass wire & reconnect the harness & carry on.
xstian wrote:
Mon Jun 10, 2019 5:26 pm
I'm not saying bypassing the relay won't work, but I struggle to believe Honda has designed it that way. Would there also not be something in the manual explaining this procedure. The pump has a pressure switch built into it, surely this is to determine when the float bowls are full?
They didn't - however If the pump doesn't get fuel it ends up sucking air. Once they start sucking air, they are useless & need to be primed. That's what it is.

Its not the end of the world, just switch onto reserve at a set distance & you will have no issues.

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Re: Fuel pump not priming

Post by Foxy400 » Wed Jun 12, 2019 7:14 pm

I've got a very similar problem with my bike. It's been away with Graeme France getting sorted but for various reasons it took 3 weeks to get it back to me, then another week or so while I derusted the tank before I got round to firing it up. So it had been empty of fuel for over 4 weeks and wouldn't start. I was straight on the phone to Graeme who told me this was a common issue. He explained the situation with the fuel cut-off relay, much as has been described here. He said unplug the relay's wiring connector, switch on the ignition and short out the black and black/blue terminals. He said he did this with a small pair of long-nosed pliers (insulated handles of course) but a piece of wire would suffice.
I'm very grateful to Suzuki416 for pointing out that this procedure is described in the Haynes Manual (chapter 4, page 4.16). That makes me much more confident about trying it, which I will be doing this weekend.

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