My son has a 2000 Bear Tracker. I think it is a 250, 2 wheel drive. Has always started and ran good. Last fall, it was getting harder and harder to start, and then finally it wouldn’t start. Checked for spark and it was very weak and intermittent.

Put a new pick up coil in and it fired right up. Bright blue spark, started and ran great. He took it on a 10 mile or so drive, and the carb came loose in the rubber tube. I picked him up and when we got home, put the carb back the way it was supposed to be and it wouldn’t start. Once again, has weak intermittent spark.
Tried a new plug.
Tried a known good external coil.
Tried a known good cdi box.

What should we check next?
Rectifier?
Could a bad rectifier ruin the new pick up coil we put in?

THanks in advance for any help!