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schwarzc

RC24/RC36 fuel cut relay - pin assignment

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Hello!

I have a very special question - can anybody with an RC 24 or RC36 tell me, which colour is assigned to which pin on the fuel cut relay plug? I know, that the wires are black, red/orange, and blue/black. And actually I know, the place of the red/yellow wire, but the photo I have does not show the difference between black and black/blue enough - so I probably only need to know, which colour is the center wire, ....


Background:, The fuel cut relay on my VF (RC15) is broken, and I shortwired it. So, when I switch on the ignition, the fuel pump starts working. However, if the bike is standing a few months, the floats get stuck, the carbs overflow and I have to follow a certain procedure to be able to start it (switch on ignition, wait until the carbs overflow, wait 2 days, start the bike)). Plus I am suspecting, that some fuel starts leaking into the oil, as it starts overflowing the carbs. So, I want to have the fuel cut relay.

Now, the fuel cut relay for the RC 15 is VERY expensive and hard to find, as there are no aftermarket parts available. However, the parts for the RC24/RC36 are much cheaper and more common. After looking at the wiring diagrams of the RC15 and the RC24/RC36, I discovered, that the fuel cut relay have exactly the same working princible, and after checking a few parts diagrams, I discovered, that some early VFRs used the RC15 fuel cut relay with the RC24/RC36 fuel pumps. So, I deduct, that the RC15 and RC25/36 relays should be interchangeable, but the pin assignment would likely be different. If it was not different, the RC24/RC36 fuel cut relay would likely be marked as successor to the RC15 part. So, I want to replace the RC15 relay with the RC24/RC36 relay, but I need the pin assignment.

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This is from the Haynes manual. Blue black apparently goes to the fuel pump on the 750F J-K models for the UK. I'm not sure exactly what you're trying to do, but I hope that helps.

IMG_3646.jpg

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Unfortunately I never owned a RC15...

If carbs are overflowing, it's time for overhaul... Even with the fuel cut-out relay the same thing could happen when bike is at idle... not much fuel being used but pump pushing fuel into the carbs => carbs filling up rapidly!

I'm not saying you don't need a fuel cut-out relay - the relay is primary meant to stop fuel gushing out in the event of a crash... so I wouldn't leave home without it 🙂

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after repeated problems, ive jumper-wired the relay on ALL my hondas with zero issues.  much faster starting if the bike's been sitting awhile and with less battery drain. don't blame the relay for your overflowing carbs.  as RC36B suggests, your carbs need attention.

 

Picture1-12-2020_054.thumb.jpg.3c07bd1bbe124ae5918091e3e246fb1d.jpg

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@Gebruiker: Thanks for the picture, but this I know already. I need a photo of the real conntector since the wiring diagram does not represent the actual situation in the connector (red/yellow is not in the center)

@RC36B and @squirrelbrains I rebuilt the carbs three times, and always had this issue. When I compared the carbs of the RC15 to the carbs of my other bikes (ST1100, FZX), I found a little detail: The FZX and ST1100 had features on the float bowls, that prevent the float bowls from opening too much. I recon, that this was done to prevent exactly this issue. (Bike is standing long, bowls run dry, needles get stuck, fuel overflows) And while I think, that a shortwired fuel cut relay might work on bikes with exactly these features (probably all bikes but an RC15), a shortwired fuel cut relay will probably cause trouble on a RC15. Because there, the bike needs the vibration of the engine to unstuck the float needles before/while the carb is filling. And as soon as I service the carbs a fourth time, I will also invent some sort of end stop for the floats. Until then, I would like to have the fuel cut relay working, to eliminate further uncertainties, ....

Edit: another indicator, that the carb is fine: As long as the float bowls are (semi) filled, there are zero issues with overflow. This does only occur, when the float bowls are empty. And even then, the float needles unstuck themselfes after sitting for 1 or 2 days, ....

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Fuel cut-off relay on wiring (4. gen. / RC36/2). From top (as to photo orientation):

  • black/blue (+ to fuel pump)
  • black (+ from fuse)
  • red/yellow (ignition pulse #4)

I agree with squirrelbrains - it takes a lot of cranking with the relay installed... I suggest a jump-wire to short the black and black/blue before cranking...

 

I don't like the bowls drying up as drying up means leaving all sorts of small particles behind after the carrier (the fuel) have gone MIA. Further, old rubber seals tend to "un-swell" => fuel leaking in unpleasant ways. Starting bike (stored at room temp) in January solves it for me.

 

 

IMG_1042.thumb.JPG.890a411e8ec1f471f71fe8976b09112a.JPG

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59 minutes ago, RC36B said:

Fuel cut-off relay on wiring (4. gen. / RC36/2). From top (as to photo orientation):

  • black/blue (+ to fuel pump)
  • black (+ from fuse)
  • red/yellow (ignition pulse #4)

I agree with squirrelbrains - it takes a lot of cranking with the relay installed... I suggest a jump-wire to short the black and black/blue before cranking...

 

I don't like the bowls drying up as drying up means leaving all sorts of small particles behind after the carrier (the fuel) have gone MIA. Further, old rubber seals tend to "un-swell" => fuel leaking in unpleasant ways. Starting bike (stored at room temp) in January solves it for me.

 

 

IMG_1042.thumb.JPG.890a411e8ec1f471f71fe8976b09112a.JPG

 

Thanks a lot! 🙂
I plan on making an "emergency fuel cut relay override switch" anyway while I am tinkering with the wiring, .... so I can choose to override the relay at all time. Or I probably make just a 3 pin connector, with the blue/black and black wires connected, that I can swap for the relay.

And yes, I dont like running the bowls dry either, but I dont have much choice at the moment (VF is to precious for me to ride daily, and the garage is a few km away from my flat) - however, that might change in the future, ....but I dont like having the bowls full, either, since this clogs the jets and was the reason for the second carb rebuild, .... 
Thanks again 🙂

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3 hours ago, schwarzc said:

 

Thanks a lot! 🙂
I plan on making an "emergency fuel cut relay override switch" anyway while I am tinkering with the wiring, .... so I can choose to override the relay at all time. Or I probably make just a 3 pin connector, with the blue/black and black wires connected, that I can swap for the relay.
 

If you really want to have a permanent semi-automatic "shortcut", add a simple relay timer triggering when the black/blue wire initially goes high (on rise).

  • Then you can turn on ignition and fuel pump will stay off
  • If you hit the start button, the fuel cut-off relay will do its work as usual - supplying power to fuel pump when engine is rotated/rotating
  • If you momentary hit the start button then timer triggers and fuel pump will engage for the set time (e.g. 10 seconds)

So for normal operation just hit start - everything works as if only the fuel cut-off was there.

After long storage; hit the start button momentarily - fuel pump will fill bowls for e.g. 10 seconds. If not enough, then repeat. Hit start button again at any time to engage start motor.

Assuming engine has run for more than 10 seconds (the delay), then if engine for any reason stop rotating, the fuel pump will turn off at once (not delayed).

 

No switch or wires-plugs - everything can be hidden. Operation of fuel pump easily verified. Easy installation - relay not costly.

 

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On 1/21/2020 at 2:36 PM, RC36B said:

If you really want to have a permanent semi-automatic "shortcut", add a simple relay timer triggering when the black/blue wire initially goes high (on rise).

  • Then you can turn on ignition and fuel pump will stay off
  • If you hit the start button, the fuel cut-off relay will do its work as usual - supplying power to fuel pump when engine is rotated/rotating
  • If you momentary hit the start button then timer triggers and fuel pump will engage for the set time (e.g. 10 seconds)

So for normal operation just hit start - everything works as if only the fuel cut-off was there.

After long storage; hit the start button momentarily - fuel pump will fill bowls for e.g. 10 seconds. If not enough, then repeat. Hit start button again at any time to engage start motor.

Assuming engine has run for more than 10 seconds (the delay), then if engine for any reason stop rotating, the fuel pump will turn off at once (not delayed).

 

No switch or wires-plugs - everything can be hidden. Operation of fuel pump easily verified. Easy installation - relay not costly.

 

Sounds neat, maybe I will try that. Thanks 🙂

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