YZ125G no spark

[Woody]

Bike started 4th kick after resto completed and ridden around briefly and parked for some time. Next time around it started and ran for a few secs and died. Then started back firing on kick over and wouldn't start.

Guys, I know very little about electrics. I put on another good ignition coil but there doesn't seem to any spark at the lead. Had a look at the manual and got the multimeter out.  From what I can see there is No resistance on the low speed coil test. There was resistance on the high speed coil test.

Which one of the two is the low speed coil (#4 or #5)?

http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1980/YZ125G/GENERATOR+YZ125G/parts.html

[alexbrown64]

Page 47 of the manual here: http://projectyz.jfn3.com/wp-content/uploads/2009/12/1980-Yamaha-YZ125G-Service-Manual.pdf  gives you all the resistances and info you need for the high and low speed coil.  It says the low speed coil has a wire that goes red to brown.  Hope that helps.  Also, i had a brand new G back in the day, an among everything that broke, a low speed coil was one of them. 
I am rebuilding a yz125K 83 model which is on this forum.  I have installed a digital PVL electrical system to eliminate all the electrical woes.  The bike was in transit from the US for six months, i fitted the PVL, timed it, put 6 month old juice in it and it started first kick and ran great.
Cheers,
Alex

[80-85 husky]

mates vespa did the same thing...the flywheel had spun on the keyway

[mick25]

mates vespa did the same thing...the flywheel had spun on the keyway

80-85 husky has a good point , one of my tt500s did the flywheel key for the first time and it was doing the same thing but still had spark but back firing something shocking it had me stuffed what was wrong for a while.
Sometimes it something small like pulling the plug cap of and losing contact at the end of the lead , found chopping a bit of the coil lead fixed it.

[Woody]

thanks Guys, was backfiring last time around some months ago but nothing this time and no spark with the plug cap removed. will check the flywheel key as suggested.

[Graeme M]

I've been through three stators on the IT175G Woody, low speed coil every time. Maybe some weakness there? Just check those resistances and see what's what.

[Ngapuhi]

I had a YZ125H back in the mid/late 80's. The backing plate screws came lose and spun the plate whilst riding, that toasted the stator coils. Would cough every kick but never fire once we reset the timing. Rewound coils, then 2nd hand stator coils fixed the prob.