Small Engines (Lawn Mowers, etc.): starter, switch or silenoid?, briggs and stratton, booster battery

Question
I have a briggs and stratton engine on my lawn chief riding mower.  when I turn the key the silenoid chatters.  The battery is ok.  The starter turns when I jump it.  Do you know what the voltage is that would come from the key to the silenoid?  I'm only getting 0.4 volts when I turn the key.  Any ideas?
jim

Answer
Everything in the system should be 12V.  The voltage should never drop below about 10V, even when cranking.  It sounds like you've got an issue with a bad connection...make sure you remove, one by one, each connection and clean thoroughly.  If you can "jump" the starter with the battery on the mower (as opposed to a second booster battery), I would assume the battery and starter are good and it's either a connection or the solenoid is defective.  Another less common problem would be a faulty keyswitch that is not providing enough power to energize the solenoid.  You can try "jumping" from the "BAT" side terminal on the solenoid to the small key side of the solenoid and see if that allows it to crank over.  If so, that indicates the solenoid is OK and the problem is between it and the key switch.  If not, the solenoid is defective.  Hope this helps.