The bike runs but has an incredibly weak spark which causes the plugs to foul like crazy.  It has no reliability,  some days it works, some days it doesn't.  Any help on the problem would be great.  Thanks.

You either have a bad connection,bad ground,bad coils,or your carbs are severly fouled up(dirty,bad jetting,vacuum leak,etc..).It's very rare for a CDI on a GS to go out.Not impossible.Are your plugs putting out a bright blue spark?IF so,it's not in the ignition.There are also safety switches that maybe sticking causing the ignition to ground out.Kick stand and clutch lever switch are the 2 worst ones.Could be a bad off/run switch or ignition.

can you tell me where the CDI is located.

You should disconnect the battery when working with the electrical system.

This image describes the test for the ignition coils (minus the first four steps, which describe how to remove the coils):



The specs are as follows:

• Primary winding resistance: 3.0 Ohm - 6.0 Ohm
• Secondary winding resistance (with plug lead end cap): 18 KOhm - 30 KOhm

For more details, you should invest in a Haynes or Clymer shop manual.