You probably have a problem with your safety interlock circuit that activates the starter solenoid. This is very common on the BX series, especially the early ones. My BX2200 did the same thing until I employed the common fix, which is installing a relay between the safety circuit and the starter solenoid. The relay is activated by the safety circuit, and the starter solenoid is activated by the relay.
For some reason, resistance builds up across the switch contacts in the safety circuit, and too much voltage is dropped across these permissive contacts, so the starter solenoid cannot get the voltage it needs to activate properly.
Edit: I guess I just said the same thing as Woody4…I made my modification several years ago. No issues since.