Motorcycle Repair: 1976 Yamaha XS650 misfiring, spark plug wire, electrical conductors

Question
I have a 1976 Yamaha XS650 that has one cylinder (as you sit on the bike, the left one) that works great.  The other cylinder has a serious misfiring problem.  When I first got the bike I noticed the spark plug wire for the right (bad) cylinder was rusted, so I replaced the wire, boot, and plug - still misfiring.  I replaced the coil, point, and advancement springs - still misfiring.  The plug is getting a spark, but the exhaust is cool and smells like gas rather than exhaust.  Plus, the exhause seems to be coming out with more force than the left (good) cylinder.  Lastly, I adjusted the valves thinking maybe the exhaust valve was opening during ignition - you guessed it, still misfiring.  I'm wondering if I have to tear the whole things apart and start from scratch, which I'd rather not do.  Can you think of where I need to go next to figure out why the firing is off on that one cylinder?

Thanks for your help.

Answer
Hi Germaine,

Always start with a cylinder compression test. Follow with a leak-down test if necessary.

Check the faulty cylinder's ignition electrical conductors and connectors.

The spark plug of the faulty cylinder may have an arc with the plug removed and grounded, however, it may not be arcing under the load of compression.

You've checked valve clearances- good job.

Get a copy of the service manual if possible.

Visit www.viragotech.com for more tech assistance.

I return tech files by email. There was no email address with your question as requested and explained in my instructions.

Respectfully,
Mark Shively