Thanks yet again.

I did order a cheap one a few months ago. Seems to have stopped working? Have just splashed out £15 on another. I will never learn.

It’s very frustrating but it can only be something simple. I must be missing something obvious.
I have no choice but stick with it…. Then can worry about the fuel side of things.. then a million other bits!

Onwards.

I got myself one of these - I wouldn't be without it. 

9089003112: POCKET TESTER Yamaha - buy the 90890-03112-00 at CMSNL

I feel I am on to something at last!

Last night I cleaned everything up again as suggested. Checked all connections again. Popped flywheel on hand tight just to check things before I tightened it up. Lo and behold a spark! Consistently. Much delight…. Left it there. Had a sleep. Checked again this morning still a spark. Great!

Tightened up flywheel. Got excited about refitting carb…. Just check one more time…. No spark. Or I should say one every 15-20 turns over. Bugger….

As a thought I slackened off the flywheel again. Spark returned.

Something must be getting trapped/shorted when flywheel on tight. No more time today but next time I get in there will look for obvious issues.

Getting closer?

As an aside my flywheel nut takes a 19mm socket but it’s very tight in there and can’t get the socket all the way “home” with my half inch drive. Worried about damaging the puller thread if socket doesn’t stay square. Is my nut the correct one or should I use a thin wall socket? I have a 3/8 drive 19mm that fits snugly but I am very aware I weed my 1/2 inch breaker bar to tighten it up. Just wondering how others get on.

Thanks, ian

Need. Not weed!

I don't have an answer to the socket/flywheel retaining nut question but I've needed to grind the wall thinner on sockets in the past for clearance in similar situations. Hopefully someone intimately familiar with this model will have an answer about the retaining nut.

I'm wondering if the points are being forced open (ever so slightlly when they should be closed) when the flywheel is tightened down? This could explain the 1.9 ohms reading (points open and closed) when you put the flywheel on previously.

My guess is the points are open too far and when the flywheel is installed and tightened the points are forced 'electrically-open' (even though visually they appear closed) on the low part of the points cam. So the points don't reliably close. The continous meter reading of 1.9 suggests this and it would possibly intermittently generate a spark.

A quick test of this theory would be to reduce the points gap a by small amount (maybe by .003-.005"). You could measure the points gap at max opening beforehand if you don't want to lose your current set point.

The timing will change slightly but that can be dialed in once you have consistent spark.

Thanks for the electrial readings. It helps to understand what may be the issue.
 

snglsmkr, that reminds me. was having trouble setting my points. found out the points were not seated in the "dial pin hole" so the cam was not able to open/close them.

UPDATE. - SORTED ( I hope)

thanks again for the input guys. Had another look today with my auto electrician friend (retired ex RR).

flywheel off. Checked all components from source coil through to and including plug. All good. So far so good.

put flywheel on hand tight spark good.   Tighten flywheel and no or little spark again. After much messing around we re-routed the wire from the points to take it away from the coils on the stator.  Success!   Flywheel tightened up and still have a spark.  Hoping that is the end of the issue.  Whether there were multiple issues and this was the last part of the puzzle I am unsure but fingers crossed all seems good.  It is still wired directly to stator but that’s for another day.  

thank you to all who contributed and supported my repair.   This is a top site. 

fuel next. Be ready!  

Wow, great thread, knowledge, persistence, help, friends, so good to hear you finally found all the issues!