Motorcycle Repair: Points ?, yamaha xs 400, xs400

Question
I have a 1977 Yamaha xs 400.It sat a long time before I got it.I cleaned gas tank and carburators.Stared and ran perfect,the first time.Got more crap into carb.cleaned tank and carb again.Put 2 filters in gas line.Runs good except.Here is the problem .Every so often one cylinder stops firing.Changed plugs,have good spark will run fine,but has a miss every now and then and back fires threw exaust.Then runs on one cylinder when it feels like.Idials ok most of the time,kickstarts first or second try.Are my breaker points messing up.If so, how to I gap them and to what degree? Or is it something else.  

Answer
Hi Gene,

The engine may have fuel and/or ignition/electrical problems that are occurring intermittently.

It's tough to diagnose these problems without being present and perfroming tests.

I couldn't find any specs for the 1977 model. It's too old for my database. Sorry!

Try finding a website dedicated to the XS400 or message boards such as those at "www.motorcycleusa.com" for others who may have the specs you are seeking.

Respectfully,
Mark Shively