Help

I just bought my son a 1986 Honda trx 125. When I first got it you could pull start it (dead battery) and it would run ok. I bought a battery and put in a new carb kit and he rode it all day. That night I put it on a trailer and drove to the deer lease. Got there and couldnt get it started. I thought that the carb had trash in it so I bought a new carb and installed it. I noticed that the spark plug wasnt getting constant spark. It seemed that it would spark a few times when you hit the start button then stop, it would then spark a few more times when you let off of the start button. I had the ignition coil checked and they said it was good. My next guess is that the pick up coil is bad but I checked it with an ohmmeter and I am getting a readying of around 100, not sure what it should be. When I push the start button it turns over and every now and then it will fire off for a few seconds. I just dont think that I am getting a good spark. Any ideas??????