1986 vfr750 running issue

I have an 86 vfr 750 f2(rc24) that is specifically the european version(German import) not sure if that makes too much of a difference in troubleshooting. The bike fires up and purrs like a kitten. then after about 10-20 mins and it gets to solid running temp for a bit, it shuts off. no spitting or sputtering, just, dead like the killswitch was flipped. It does the same traveling on the highway. driving just fine and dies completely, in gear and everything. My first guess was maybe R/R, since they're prone to failure. I tested it with a DMM and it's output on the battery is solid, all the way til it cuts off, which shows no fluctuation of the voltage while pushing charge. It's doesn't hard idle at all, and runs about as good as a 28 year old bike could be expected to run in top shape. My next thought was maybe a faulty relay. i pulled the seat and saw the fuel cut relay. i pulled it, jumper'd it, and it did exactly the same, so that relay is fine. I also piddled with the fuel system understanding how it works from testing as well as studying from online and have determined that the fuel system is fully functional. My next plan is to pull the tank to be able to do my next step of troubleshooting: run the bike til it shuts off, open into a couple of carbs and spray in starter fluid to see if it fires at all, which if my guesstimation is correct, it won't. because it has air, and it has fuel, so it must not be getting fire by my logic. my deal is, if a coil pack has gone bad and breaks circuit, it should still run on 2 cylinders, albeit god-awful. i don't think the odds of both coil packs faulting simultaneously are very high, so could it be a cdi box issue? I'm new to bikes and haven't aquired a lot of knowledge on their workings but i do know a bit about working on stuff and pretty good at figuring things out. I was hoping maybe one of you guys had run across this issue before and it just clicks that you know what it is. I'm sure I can figure it out eventually but I don't get a lot of free time to spare between working 60 hours a week, school 16 hours a week, having a 1 year old, and a pregnant wife so my time isn't something I have a lot to spare. Thank you guys in advance.

 

It it dies suddenly, sounds like bad/dirty kill switch, check continuity of switch as you flick on and off and wiggle side to side. Contacts and be cleaned and burnished.

 

I believe that would be the case if it were intermittent failure but this is rather consistently timed. operates 100% for 10-15 minutes, then after 10-20 mins of sitting it fires right back up with no mechanical change of the bike for another 10 minutes, rinse and repeat, which is what makes me almost certain heat is going to be a factor in the issue. advice is noted and will be carried out to eliminate the possibility regardless, thanks.

 

Your right, but you need to look for a single source that will kill engine. Carb/gas would sputter. Coils and triggers separate for each bank. Common power comes from R/R to stop/start and ignition switches. BL wire in the diagrams. Possibility bad R/R not supplying +12vdc to black wire, or bad connector that gets hot. Diagrams are from my '83 service manual, but should be close to yours. Honda use same arrangement on my 03.


Follow black wire from R/R to junction (dot) to ignition switch and stop/start switch. Must have +12vdc to run. If you can put you meter on this wire after it quits, then you will know.

 

Two details, other too hard to read.


Quick test would be does starter engage after it quits? (Starter relay gets power from Bl wire)

 

Yeah. Everything else functions properly but doesnt seem to make an effort to fire when it's in "cooldown". This is what leads me to believe it has to be something to do with the firing system, but it has to be something that causes a total failure in the ignition system all at once.

 

hey Xoeclyus, did you find your running issue yet? i have a 1986 vfr 750 interceptor doing the exact same thing. swapped out regulator, old one was getting super hot, did not help still dies after 10 to 15 mins of riding.

 

Nope sure havent. Im thinking it may be cdi box issue but due to my little free time it may be a bit before I can check that out.

 

It is a bit of a pain to setup but you could run a new wire from the battery directly to the coils, this will take all the existing switches and wires out of the equation, just remember to connect the wires, take it for a ride and then disconnect the wires, or you can make it more permanent by fitting a relay controlled by some ignition on power supply. At least this will tell you if it is a power supply problem to the coils. If not you then need to look at pulse coils or CDI, most likely not pulse coils though because both wouldn't fail at once

 

When i had a very similar issue i determined that it was one of the pulse generators, working fine when cool but going open-circut when it reached normal operating temperature.

 

Go try it again today while it's so cold out and see if it runs longer. And you might try opening the fuel cap and leave it open, just in case the tank vent is clogged, although it does sound like an electrical issue. The only electrical issue that can 'heal' itself is a cracked solder joint that opens up when hot and closes when cold. Whereabouts are you located, i'm just outside huntsville.

 

Yeah not much luck with that I work 12s all weekend school for 16 hrs mon then 12s rest of the week. Like I saidni dont get much free time at all.

 

I think squirrelman man be on to something. Prolly gonna drop it off at my uncles and let jim piddle with it he has lot more free time and be happy to make 75 buck for his trouble