Starting problem

Used the Bonnie on Thursday and all well. Tried to start yesterday morning and instead of that initial starter whir followed by the crackle of the exhaust, just continuous starter whirring.
Checked fuel - plenty in carbs and flowing fine. Took LH plug out to check for spark and nothing initially but then on third go there was and bike tried to start on one cylinder.
Changed plugs and the bike fired up fine. Plug looks normal colour, slightly brown and clean and gap was spot on.
Not sure what caused this but fingers crossed.

 

Hi Dave, should have added that I charged the battery up to 100% before testing for a spark. Out for an 80 mile run today with no problems - plenty of stopping and restarting. I replaced the plugs when I bought the bike last year and changed the stock red ngk caps for black ones. On checking yesterday I noticed that the LH ht lead has insulating tape wrapped around it so have ordered a new pair from squaredeals - just as a precaution.