Starting Issue (another☺)

Great description of your problem. Walking through your write-up, and the sequence, it appears that the extra amperage from the jump may be the difference between starting an not starting. Hmmmmmmm..... is right

Just thinking out loud - Can you load test your battery to see if the volts are OK, but the amps are low? Also, could there be any corrosion on the battery terminals or a broken terminal that responded well to the jump? Even though you wiggled the wires, you might still have an intermittent short or ground to track down. If you have a wiring diagram, it would be good to pay special attention to the ignition circuits. I would also try to get Tune ECU or Dealer Tool to see if there are any error codes stored in the system. If there are, they might lead you right to the problem. Good luck with your gremlins.

 

Carbs or EFI? The difference is igniter or ECU but hopefully irrelevant. I assume kill switch not thumbed and ignition switch given an occasional squirt of cleaner or WD40 to assure terminals kept sound. They can corrode but that would likely result in no starter as well as no ignition.

It is slightly odd that your battery is turning it over and that it then fired when jumped. That suggests a dodgy connection in the ignition circuit. Multiplug in the headlamp shell and one in the harness under the tank. Your main earth strap connects to the motor via a bolt on the underside at the rear of the gearbox. A slacken, wiggle/clean, re-tighten would not hurt. .....but that would likely have inhibited the starter motor and sidestand switch and clutch lockout would also prevent any turnover.

So........switch on ignition and check for battery voltage from the +ve side of the coil to the frame.....or direct to battery -ve if Earth not proved. If you have power there you know it is either Igniter/ECU (expensive and least likely) or one of the coils I.e. the ignition coil that can go intermittent as it dies or the crank position sensor coil that fires the ignition. If you have a multimeter you can check resistance readings for the coils.....something like 16-18000 ohms across the main HT windings and just under 600 ohms for the pickup coil (easiest measured where it plugs in adjacent to the battery)

Let us know what you find.....

 

Some years ago when I had a Ducati 900GTS I started getting exactly the same problem, starter would spin the engine fine but no sign of it firing at all but if I then tried the kickstarter it would fire up straight away, cured it on that simply by fitting a new battery.

 

I have one additional suggestion. If a new coil was fitted 'recently' don't start with the assumption that it is working properly. Most of us would start with that assumption and then start looking at everything else first. Occasionally, you do get new parts that are 'bad' right out of the box. How recently was it put on, in relation to the problem showing-up?

 

You say 12.3v in your op
It needs 12.6v otherwise it won’t start

 

Hence my question about carb or efi but if it spins it SHOULD start. I would be for checking all the coil and leads are in spec.
LT .7 ohms
HT 15-16,000 ohms
Leads 5,000 ohms (actually the cap suppression - leads themselves negligible)

If they all check out the problem is the trigger mechanism to collapse the magnetic field I.e. pickup coil or igniter.

Additional thought is seat base pressing on igniter....a known failure problem.