Hello folks,
Following on from my indicator post, as I had my multimeter out and the bike was difficult to start when not-cold, I measured the resistance of the source coils and pulser (the spec values coming from my Haynes manual):
Pulser: White/Red to Black - 12.1 Ohms (in spec compared to 12.4 Ohms)
Source coil 1: Brown to Black - 288 Ohms (out-of-spec compared to 420 Ohms)
Source coil 2: Red to Black - 12.4 Ohms (just in spec compared to 13.6 Ohms)
If you could help me once more as source coils are flipping expensive if you can find them:
> I think the 420 Ohm coil is Source Coil 1; the coil that sits next to the base plate. Is that right?
> I would imagine that a resistance of 288 Ohms vs 420 Ohms will not be helping with respect to my not-warm starting problem. But to avoid chasing shadows and unnecessary expense, is such a value likely to be a significant problem (I assume it must be otherwise Yamaha would have specified a larger tolerance)?
I have measure the ignition coil too, and that was OK.
As always, many thanks in advance for any advice.
Mike

 

Searching for spares, I found some photos that show source coil 1 with brown wire and source coil 2 with red wire. So I’m now sure of what needs to be replaced :-)

You may want to consider posting up what the bike configuration is and problem(s) you are having.

288 is a long way from 420 so is a likely cause. But you say Not Cold then later say Not Warm. Is that pretty much the same thing. I'd expect it to be lacking spark from cold "if the low reading on the brown is the cause" & if it changes when hot I'd think it'd only get worse if it changes at all. It's all magic hidden in there. Sourcey thing #1 will be the brown then topped up by the red at revs I think. On my 490 the red coil was faulty so just ran it off the brown only using a cdi box of a yamy scooter & ran as good as it ever did still stretching my arms lol. Sorry, that's not helping is it. A peak meter I use is a great way to test kick voltage which I always look for 160 peak volts or 80 on an ordinary meter. Good test might be to push start it to compare with kick speed. Is choke working as it should. I tend to use an adjustable speed reverse drill on the flywheel nut nowdays as can slow it to about kick speed & if no spark then speed it up to see if magic appears which in my book related to the main source coil voltage. Cdi spark never look great but if it's visible it's gotta be good to go--but I could be wrong.

RT325: Thanks for that. Sorry for my mixed terminology. When bike is been standing overnight or longer (not warm), it starts second or third kick off the choke. If I've run it and restart 2-3-4 hours later, it can be a pig to start (not cold). I did put that down to bad starting technique by me, but the resistance measurement got me wondering whether there was something else that was contributing.
Pabdt: Happy to share the back story to this:
The engine was totally rebuilt by one of the most reputable rebuilders in UK 500 miles ago following a seize (I did put some posts up about that last year). It was rebuilt with 0.5mm oversize and it wasn't "tuned" in any way. I ultrasonically cleaned the carb, replaced all the jets and float bowl with genuine mikuni (standard sizes). Oil pump rebuilt by another UK expert and flow measured as good. I have no doubt the mechanicals are OK. Plug colour looks good to me and it goes well when warmed up and off-choke.
I decided to put my indicators back on as I'm now only using the bike for street and not dirt. I remembered that the indictors always had a weak flash so I thought I would check the wiring and the earth just to make them as good-as-they-can-be (my other recent post relates). That done, my multimeter out and wondering what to do next, I thought about my starting challenges.
As above, when the bike has been standing overnight or longer, it starts second or third kick off the choke. If I've run it and restart 2-3-4 hours later, it can be a pig to start. So I thought I would check the resistance of the magneto and ignition coils. And that revealed the low resistance on source coil 1 (all others measured ok). For sure I’m no expert, but a weak spark seemed like it could be a possible cause of my starting issue.
As the source coils are rare and therefore expensive, I wanted to make sure I ordered the right one (I’ve now figured this out) and was interested to know if the low resistance was a likely cause of the starting issue and spending > $100 would be worthwhile.
That’s my story! Thanks again.

Before spending the money, I would test the coils when cold, then again when hot. If there is no substantial difference, the hard starting is not likely caused by the coil.

Check other coils too, resistance will change with temp but you should be able to get a sense.

Also, make sure your spark plug gap is set to 0.020" to 0.024" max on these bikes.  Narrower gap is requires less voltage and modern plugs usually come gapped at 0.032" or so which is too wide.