I have a 17hp Briggs that will start sometime but other times will not turn over . Put new starter on it and machine did the same thing.
agree, could be battery. you need to see if the next time it wont crank what the battery drains down to. next time it doesnt want to put a volt meter on the battery then crank it.
How volts are you getting on the battery? How old is the battery? Lawnmower batteries have a life span of 1-3 years. Will it turn over if you jump the 2 posts on the starter solonoid?
Now if its a bad battery why would it turn over some times and other times not. This is the reason I would be looking for a switch problem or bad connection.
It happened to me many times. Changed battery and was fine. Tried old old battery on other mowers same as when it was on the mower it came off of.