No spark on the spark-plugs

[Thomas Nilsson]

Hi!
I bought a Yamaha XS400 12e 1983 last year and it was running fine but needed service and new sealings in the front fork..
The old battery was not keeping the power so I had to buy a new one but when I tried to start the bike it will not start...?
The starter is running fine and I've checked the fuses under the seat and it looks good.
When I checked the spark plugs there is practically not any spark ( a fade spark every ten seconds maybe......:-( )
Are there anyone that has got any idea? Is it the CDI-box?
/Thomas

 

[JPaganel]

Could be a number of things.

Start with cheap and simple - check battery cables, connections at the starter solenoid, grounding points, connectors to the coils and CDI. Look for corrosion and cruddy wiring. Make sure everything is clean and tight.

Check coil resistance - manual tells you how.

Are your high tension wires any good? Maybe replace them. How do plug caps look?

A CDI can't really be tested without a bunch of special equipment. If you have a spare, you can swap it in to see if it makes any difference, but that's kind of a last resort. So, you check everything else first.