Member Contributer CBVFRbikeboy Posted May 19, 2016 Member Contributer Share Posted May 19, 2016 I've just discovered the fuel cut-off relay on the 750 has shat itself. I have a spare to use, but I was wondering what the function of the relay is? From what I can gather, it's just a faster acting relay similar to the indicator unit? It just cycles on and off at a quicker rate? Just wondering if there might be a cheaper alternative aftermarket solution. cheers ian Link to comment Share on other sites More sharing options...
Member Contributer Forbes Posted May 19, 2016 Member Contributer Share Posted May 19, 2016 Most fuel pump relays are there in case of an accident, when the motor stops so does the fuel, otherwise a potential fire hazard. On fuel injected cars there is a return fuel line that relieves pressure at low speed, so no flooding, and fuel pressure also has a bearing on fuel mixture, to rich or lean etc. Because the VF is carburetor fed with no return fuel line I would think this the reason for the pulsing of the pump. It would be very easy to presurise past the needle and seat thereby altering the fuel to air ratio. My advice, keep the stock relay. I have personally seen the negatives of no fuel shut off, not my own... Sent from my HTC_PN071 using Tapatalk Link to comment Share on other sites More sharing options...
BluRoad Posted October 20, 2016 Share Posted October 20, 2016 I think I hear you saying that the relay is pulsing the pump? I don't think that is the case. The pump sounds the same when it's connected directly to power. The relay's function is to allow the pump to run only when the engine is turning over (including via the starter motor). As Forbes noted, it's there in case of an accident. Sorry, I don't have any idea for a substitute. JOE in IL V4 Dreams (.com) Link to comment Share on other sites More sharing options...
Member Contributer Forbes Posted October 20, 2016 Member Contributer Share Posted October 20, 2016 I've read somewhere that the two cdi's run the revcounter and the fuel pump independent of each other, hence why the revcounter is a bit erratic on these bikes. I would think the relay would have some sort of capacitor on the field coil so it stays connected while one of the cdi's is not firing, so if your pump is pulsing maybe the relay is faulty? It would be a very quick on/off cycle though. My bike is not running so I can't test this theory...don't think the Clymer manual would be that specific but I'll look!Sent from my HTC_PN071 using Tapatalk Link to comment Share on other sites More sharing options...
Member Contributer Captain 80s Posted October 20, 2016 Member Contributer Share Posted October 20, 2016 The "fuel cut" relay is a safety feature only. It does not control how the pump pumps, just if the pump pumps. I install parallel toggle switches on my bikes for a couple reasons. - I can just flip the toggle after I have drained the carbs (winterize, carb work, etc) and re-fill the carbs without having to crank and crank. - I can just flip the toggle WHEN the relay shits itself somewhere in the middle of nowhere. There are a few who just bypass it, but as long as I have the toggle I leave it there for safety. Link to comment Share on other sites More sharing options...
squirrelman Posted December 16, 2016 Share Posted December 16, 2016 I delete that relAY ON ALL MY Honda bikes after my first relay failure and never had a problem since, even dropping a couple times. Much faster starting and less battery drain, especially when the bike hasn't been ridden in a few weeks or months. Do the relay by-pass described in the FSM. A toggle switch like capt 80's is the best deal. Link to comment Share on other sites More sharing options...
Ascalon Posted December 20, 2016 Share Posted December 20, 2016 The CF318, from the early CBR600 and VFR750 models, works on a VF1000 FF with the three wire fuel cut off relay, the CF304. I'd imagine it should work on the VF750F too. Link to comment Share on other sites More sharing options...
atx Posted December 26, 2016 Share Posted December 26, 2016 The early bike fuel cut relays have a different style connector than the f2's, apparently the early CDI gives out a slightly different signal which is basically just an extra tach signal for the relay to see. Pretty sure the later cdi's send out a different signal for the fuel cut relay, not just a tach signal. There is no extra controlling or anything done by the early relays thanks to it seeing the rpm's or anything, still just on if it sees any revs at all and is a more annoying connector setup than the ones. This modified later style relay came with my bike in a box of parts, i was having issues with my bike and tried swapping it in to see if it made a difference, seems to work just as well as the original one which is no longer made. The nice thing is in the future i can buy a new compatible relay for $30 made by K&L, part 18-8783. Slides right into the original fuel relay rubber holder doodad. http://www.ebay.com/itm/New-Fuel-Cut-Relay-VF500-VFR700-VF700-VT700-VF750-VT750-VF1000-VF1100-GL1200-/311708810857?hash=item48934afe69:g:0yQAAOSwTA9X7MCo&vxp=mtr I dig the extra switch idea for redundancy on the road and such. Very cool. With the side cover being quick release and all it wouldn't even be visible if you tucked it in there. Could even toss in a second switch as a fuel pump kill easily enough too. Link to comment Share on other sites More sharing options...
Lloydo Posted July 25, 2017 Share Posted July 25, 2017 Hey guys, I have an 84 750 interceptor that has run flawlessly for the 23 years I have owned it, I absolutely love the bike. Unfortunately I completely killed the battery the other day as I pulled the key out in a rush and left the headlight powered (old worn out key) and had to boost it. After boosting I could not get the the bike to idle let alone produce any significant rpm. The longer I left the boost/charge unit attached the better it idled and I got to a point where it would idle by itself and managed to limp home. I find the bike idles better without the relay attached, it's the CF 304 pictured above and I plan to purchase the aftermarket unit. I would like to "jump" the relay and see if in fact that is the problem, 12 volt electrics is my downfall however. The plug has 3 wires white, blue and black. The blue and black have 12 volts the white no volts, I didn't check any continuity. Can anyone suggest the best way to bypass the relay so I can see if the engine will produce power. Let me know if you think I'm way off on the diagnosis but it was running sweet before the battery died. thanks. Link to comment Share on other sites More sharing options...
schwarzc Posted September 27, 2017 Share Posted September 27, 2017 On 26.7.2017 at 1:40 AM, Lloydo said: Hey guys, I have an 84 750 interceptor that has run flawlessly for the 23 years I have owned it, I absolutely love the bike. Unfortunately I completely killed the battery the other day as I pulled the key out in a rush and left the headlight powered (old worn out key) and had to boost it. After boosting I could not get the the bike to idle let alone produce any significant rpm. The longer I left the boost/charge unit attached the better it idled and I got to a point where it would idle by itself and managed to limp home. I find the bike idles better without the relay attached, it's the CF 304 pictured above and I plan to purchase the aftermarket unit. I would like to "jump" the relay and see if in fact that is the problem, 12 volt electrics is my downfall however. The plug has 3 wires white, blue and black. The blue and black have 12 volts the white no volts, I didn't check any continuity. Can anyone suggest the best way to bypass the relay so I can see if the engine will produce power. Let me know if you think I'm way off on the diagnosis but it was running sweet before the battery died. thanks. Connect black and white, isolate the blue wire. The fuel pump (fast ticking noise) should work, when you turn the ignition on. If the ticking noise stops, after some time (~20 sec), everything is good. If it continues, your carb needle valves are stuck in open, and fuel will come from the carbs. Link to comment Share on other sites More sharing options...
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