First of all thank you guys for your time!
I picked up this bike for 300 from a local farmer... it has been serviced every year at the local Honda shop but stopped running last year and he didn’t want to mess with it.
I took it to my shop and figured out it had no spark. So I started back tracking everything and figure out my CDI box was bad. So I ordered a new CDI box and figured I order the coil and plug as well since they are fairly inexpensive. I put everything together and I had spark! I put the plug back in and turned the fuel on and it fired for a second then died...
After a few moments I figure out I had no spark again... I back tracked it to the CDI and thought maybe I got a faulty one. I ordered a new one and put it back in and had spark again. Fired it up and once and it did after a few seconds and now I have no spark again... What would cause be to have spark when testing it to the head and then once it starts it what I assumes fries the CDI. I bought a third CDI and have spark again but I do not want to put it back in and fire it up until I figure out why this is happening. I feel like get two faulty CDI boxes is highly unlikely.

something that is worth the mention is that the farmer did a pretty good hack job on this thing... the orginal key and start button are out and a regular turn key ignition is in its place with about 6 or so wires twisted together and attached to the ignition post on the switch.

 

Fit a proper ignition switch for a start. Always check the wires to the CDI before fitting a new one. Main wire to be absolutely certain is correct is the earth, fit a CDI with a bad earth connection to it and you will blow it the first time you start up. There were four different CDIs for the 300 model depending on year, only the last one had a different plug, so the first three look interchangeable but won't work. The colour of plugs and sockets need to be the same, white, red, or green, unless you are fitting aftermarket CDIs, which all seem to have white sockets, but need to be be the right one for your year. Another thing that will blow a new CDI is a faulty voltage regulator, check voltage across battery does not go above 15v when you do get it started, if it does, shut down right away and fit a new regulator before starting it again.

 

I will check those when I get back to the shop. Are the CDI boxes usually ground at a certain location?

 

Are the CDI boxes usually ground at a certain location?

Probably will be, but I always test the earth wire at CDI plug, preferably with a high wattage test lamp, one wire on battery pos the other on the earth wire at CDI plug, nice bright light = good earth. Not sure without the wiring diagram, but think green/white is earth to CDI on the 300. Black/white is earthed by kill switch, so this can be checked at the same time, as can pale green/red which is earthed by the gear pedal, some earth in neutral ,some earth when not in neutral, some may even be positive, depends on year of bike, but there should be a change when you put it into and out of neutral.