One bike at a time-okay the one that seems to hold a charge-what charge does the battery hold? You should take a volt meter and put it across the terminals (pos to pos, neg to neg) and take a reading-it should be between 12-14 volts. Next if you can, take it (the battery) to a auto supply store and have them do a load test on it, or get a cheapy load tester from Harbor Freight. If the battery checks out okay, then your problem is with the starter solenoid or with the starter circuit or some component there in.
Now for the second atv-if this one's battery holds a decent charge, then start testing the starter solenoid-put a screw driver across the 2 terminals-if the vehicle starts (with the key on of course) then your problem is with the solenoid. if not start diagnosing the wiring at the starter
Get a manual for the 450 foreman machines, it will save you loads of money and give you the exact testing procedures for the machine for each electrical component. Manuals run about $30 new or $15-20 on ebay (when available).
