Fuel pump not priming

[xstian]

Hi, Ive had a bit of a problem with my nc29. The bike got low on fuel and started to conk out, I turned the tap onto reserve, but the bike still stopped and would not start. After about 15min of messing about the bike suddenly fired up and I manged to get it home.

After a bit of investigaring Im confident the pump will not fill the carb float bowls if they are empty. It seems the pump relies on back pressure to know when the float bowls are full. I had the pump on the bench and cleaned it out. If you put your finger over the out let with the pump running it stops, take your finger away and the pump starts up again. So it seems to work.

Any ideas?

[xstian]

I assume the float bowls are vented. If these where blocked could that cause the pump not to prime?

[Suzuki416]

This does happen on the NC29. You can jump the relay to prime it (its in the Haynes Manual). I used to carry a wire in the boot to do this very job.

[CB1pod70]

To expand Suzuki416's post, the fuel pump is fed from a relay which is connected to the coils so that the pump only gets power when the engine is running. You can bypass the relay (if you need to prime the carbs) and the pump will then work without the engine running. The idea is that this is a sfety feature to cut the fuel supply in the even of an accident

[royster81]

To expand Suzuki416's post, the fuel pump is fed from a relay which is connected to the coils so that the pump only gets power when the engine is running. You can bypass the relay (if you need to prime the carbs) and the pump will then work without the engine running.

I didn't know that,

[xstian]

To expand Suzuki416's post, the fuel pump is fed from a relay which is connected to the coils so that the pump only gets power when the engine is running. You can bypass the relay (if you need to prime the carbs) and the pump will then work without the engine running. The idea is that this is a sfety feature to cut the fuel supply in the even of an accident

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.

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.

I believe my pump must be at fault? Although the bike starts and runs fine at all other times. I had the pump on the bench to clean it out and I could get it to work correctly on the bench. When I reinstalled it I also bypassed the relay to test the pump and I did get it to prime.

So, either I've fixed it with a flush and a clean out or its an intermittent fault that is going to recur when I next get low on fuel or the relay does do more then just supplying the pump with continuous power.

I'm going to Scotland on Thursday to do the North Coast 500 on it, so don't really want it breaking down on me. I've bought a replacement pump form ebay, but it seems they don't get very good reviews. I've also got a spare generic relay I can swap in too. Both of these fixes looks like it involves cutting the loom, which I don't want to do unless I know it will fix my problem.

I've also replaced the contacts in the pump. Also is the tube coming off the plastic cover just a drain?

[Suzuki416]

Right ok - this is really easy...

If you get to the point of the engine dying (after switching to reserve) then YOU HAVE TO start with FULL CHOKE & zero throttle.
If that doesn't start you then yep the fuel pump is empty & needs to be primed - hence the jumper relay in the boot - lol

[Suzuki416]

[

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.

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.

I believe my pump must be at fault? Although the bike starts and runs fine at all other times. I had the pump on the bench to clean it out and I could get it to work correctly on the bench. When I reinstalled it I also bypassed the relay to test the pump and I did get it to prime.

So, either I've fixed it with a flush and a clean out or its an intermittent fault that is going to recur when I next get low on fuel or the relay does do more then just supplying the pump with continuous power.

I'm going to Scotland on Thursday to do the North Coast 500 on it, so don't really want it breaking down on me. I've bought a replacement pump form ebay, but it seems they don't get very good reviews. I've also got a spare generic relay I can swap in too. Both of these fixes looks like it involves cutting the loom, which I don't want to do unless I know it will fix my problem.

I've also replaced the contacts in the pump. Also is the tube coming off the plastic cover just a drain?

Nothing wrong with your pump - just take a relay bypass wire.
I've had my CBR for 16 years - still on the same pump (not sure they ever go wrong) - & this has happened to me at least 20 - 30 times. Its all down to when you catch the switch to reserve. If you do it at the first hic then is 80/20 you can carry on - wait for a big HIC & its usually too late... lol

[xstian]

[

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.

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.

I believe my pump must be at fault? Although the bike starts and runs fine at all other times. I had the pump on the bench to clean it out and I could get it to work correctly on the bench. When I reinstalled it I also bypassed the relay to test the pump and I did get it to prime.

So, either I've fixed it with a flush and a clean out or its an intermittent fault that is going to recur when I next get low on fuel or the relay does do more then just supplying the pump with continuous power.

I'm going to Scotland on Thursday to do the North Coast 500 on it, so don't really want it breaking down on me. I've bought a replacement pump form ebay, but it seems they don't get very good reviews. I've also got a spare generic relay I can swap in too. Both of these fixes looks like it involves cutting the loom, which I don't want to do unless I know it will fix my problem.

I've also replaced the contacts in the pump. Also is the tube coming off the plastic cover just a drain?

Nothing wrong with your pump - just take a relay bypass wire.
I've had my CBR for 16 years - still on the same pump (not sure they ever go wrong) - & this has happened to me at least 20 - 30 times. Its all down to when you catch the switch to reserve. If you do it at the first hic then is 80/20 you can carry on - wait for a big HIC & its usually too late... lol

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.

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?

I've also owned this bike 7 years and gone into reserve many times and never had this problem before.

[xstian]

I wonder if the problem on your bike could be the relay is not giving enough voltage to the pump so it won't always run/prime. Bypassing the relay would give the pump full 12-13 volts. Have you ever tried a new relay on your bike?