1986 RC25 suddenly dies...looking next steps

So I have completed my VFR750 86 build, but it has a fairly common problem of just dying

I have seen on a couple of threads this problem , but am failing to see the solution , or specifics

Basically my bike doesn't like to fire with a lowish(12.4v battery)

I just put in a lithium. Fires straight up,less than a swing and she is happily bubbling along
Went for a shakedown ride today. 2km...then she just straight died. As I was on a hill I tried bump starting..instant start.
Voltmeter reading constant 14.2v
I rode for another 500m and she died again.
Battery (lithium was on 13.2) nothing. Swinging like crazy
Went and got a mates cdi off his running bike (I had it off specifically in case of this problem)
Still nothing.
Battery is now around 12.4.
Swopped in a lead acid battery that had been on the charger overnight.
Nothing
Changed back cdi to mine
Nothing
Tried jump starting lead acid off car
Nothing
Got towed home
Going down my driveway for shits and giggles I tried jump starting her
Vroom then died
By this stage I was out of ideas and batteries

What are my next steps... ?

pulse coils in tappet cover?
Stick another earth somewhere on frame?
Speed governor box? (jap import model)

Any help will be useful as I havnt found any of the threads regarding this to be solved?

 

Had a similar issue last fall, new rectifier / regulator solved it. Check wirirng around old one for heat damage and melting......

 

Thanks mate,not sure this is it.. I had changed the rectifier to a new one, steady 14.2 when running

 

Check the connectors to your stator and make sure you're not cooking them and dropping in amps, just because you have the volts doesn't mean you've got the amps. Could also be that where you're measuring the volts isn't actually hitting the rest of the system. Like if the red connector by the battery is crispy, and you're measure on the r/r side and not at the battery. Common rewire of the r/r is to run it with its own fuse to the battery positive, skip out that red connector altogether.

 

Mmm.good things to consider.... thanks.

Not sure why that would cause it to immediately die with no warming?
(Looking to learn here)

My voltmeter is connected direct to battery.
I like this idea of wiring rr direct to battery.

My mate rekons it the pulse coils in the tappet cover. I've seen this mentioned a few times... merit?

 

Does your voltmeter fluctuate at all between idling and revving, or does it read steady 14.2 all the time?

Both pulsar coils rarely fail at the same time if they are working when cold.

 

this is one sign of trouble.







>>>>>>> measure ohms on the pulser coils both cold and hot.<<<<<<<

 

Mmm. Bike fires up and idles beautifully.
I am getting a pretty constant 14.2 regardless of the revs. 14.10-14.3
I need to get her fired up and see the temp of stator wires. These have been soldered direct to plugs into rectifier (massive)

 

OK, the stator and r/r are both fine. check the main ground wire to frame and fuel pump operation.

 

Thanks. Is it a good idea to add another earth ?
(new battery cables, both positive and negative)
Fuel pump is off a thunderace, seems to be pumping well.. will check...fuel relay perhaps... do they work intermittently?

 

pump relays often fail, can be wired directly.

a bike that cuts out electrically does it quickly, but a bike thats running low on fuel gradually stutters and dies slowly

 

Yeah, thats what i figured, and this was instant

 

Replaced pulsar coil sender? from a known running bike. When I take for a test ride...probably weekend...I'll take the cdi as well.

 

Ok been doing lotsa reading and i'm now pretty sure its the Pulse generators

exact probblems as this thread
https://www.vfrdiscussion.com/index.php?/forums/topic/97900-86-vfr-700cc/

Anybody have a set they know is good, that they would sell?

 

Try measuring the resistance when the pulse sensor is cool and again when it’s hot, there should be a small difference 10 ohms maximum

Electrex may be able to help with replacement parts

 

Good to know..thanks. willchevk

 

Ok contacted Etectrex, awaiting reply...which they say can take up to 4 days

Has anybody here ordered from them before? This is what they offer, wonder which will fit?
I have not taken my cover off yet, does soemone perhaps know which hole size could work?