Motorcycle Repair: Yamaha XV250 CDI problem??, regulator rectifier, air gap

Question
1989 Yamaha XV250 Route 66 (Virago). This bike refuses to fire the front cylinder. Seems to run pretty good on the back cylinder which indicates to me that it is not a carb problem. I get NO spark at the front cylinder. I have had the coil tested and it tested extremely good. The pulsar coil should be good since the rear cylinder runs. I think I have narrowed the problem down to the CDI box or maybe the pickup points at the stator (to fire the pulsar coil). Is there any good way to test/repair the CDI unit on this bike? Also, how would I check to see whether the four points needed to pulse the pulsar coil are good? And, lastly, where can I get a CDI unit (black box) at a price that is reasonable enough to warrant fixing this bike. It is in pretty good condition other than it only runs on one cylinder. Seems a shame to throw out a perfectly good motorcycle because the part to fix it is priced so ridiculously high. Oh yes, one other anomaly I have noticed. Occasionally, there is a very brief flash of brilliant light generated through the lighting system (noticed in headlight) which seems to happen most often when reving the engine. Doesn't seem to occur if the rpm is kept constant. Doesn't always occur on reving but seems to happen when reving. The brightness of the lights seems to increase significantly on reving up but past a certain rpm stabilizes and doesn't get brighter. That is a little concerning to me but the bright brilliant flash is what I am really puzzled by. Could the regulator/rectifier be failing intermittently? I thought those things either did right or failed altogether. Well, thanks in advance for any help and guidance you might be able to give! I would sure like to get this one going as it will introduce a new rider to the sport.    RHo7172854@cs.com

Answer
Hi Raymond,

I agree with you about the CDI being defective. Pick-up coils can be tested quickly by measuring resistance and continuity. You could also check the air gap between pick-up and trigger, though I doubt any parts have moved.

Try www.electrexusa.com for the finest quality electrical parts available. Also try "www.bikebandit.com" for parts, price comparisons, and microfiche.

I suspect the bright light effect is a spike. I would quickly test the charging system for defects. See Electrex USA's troubleshooting chart.

Great problem description.

Respectfully,
Mark Shively