I have a big red 350 ( 1990s model) it will not start elect/kick or jump start. it just wont start.Petrol is geting thrught ?.useI on the farm . and it stop starting by the electrircal, so I kick started the bike and now it just refuses to start. I have cleaned the spark plug which was black but U guessed it no start. I am going out to get a new spark plug ,but suspect it is more than just the plug.? Wally ps I am in Austraila

Well, if it stopped starting with the electric start, but would kick...and now no longer kicks....and the plugs are as black as you say...
One of 2 things are most likely your problem.
The battery is likely extremely low or dead right now.
With no load it may still read 12V, but don't go by this.
The battery itself is probably toast OR the charging circuit (alternator/rectifier/regulator) isn't working.
Put the battery on a charger overnight, and see if it starts in the morning.
It may be flooded from several start attempts, so it might be a bit of a stubborn start.
If that doesn't work, post a reply to this thread.