Motorcycle Repair: honda ignition, honda twinstar, honda ignition

Question
I have a Honda twinstar #MC0105BM10922 built 11/80 with about 12,000 miles on it. I use it for short trips and to get the mail. About a year ago it sometimes wouldn't run on one cylinder at startup. Riding at low speed I would disconnect the left plug wire and then reconnect it and then it would run O.K., then after a period of time it quit and wouldn't start. The spark at the end of the secondary wires is weak. It will jump from the wire to ground, but not through the spark plug connector or across a plug. I switched the coil with no result, then the "brain box" also with no results. I also cleaned up all the electrical connections, still a weak spark which I am getting whether the brain box is connected or not. If I disconnect the relay near the brain box I lose all spark. I also don't appear to be getting much voltage at the feed to the coil.

Many thanks in advance for any help.

Joe  

Answer
Hi Joe.
 Your problem has never been in the brainbox.  It is in the ignition system, however.  When you have failures, they are only in one cylinder.  Changing the coil didn't fix it, so the problem is in the wiring.  Check the wiring, for that coil, with a multimeter.  It sounds like you have an intermittent short.  The repair manual has the schematics and specs for you.  Test the coils in accordance with those specs.

 Check the voltage at the battery leads while the bike is running.  If it is in the coil then you will be getting less than 13 VDC at the leads.

Start there and see what you find.
Good luck.
FALCON