I feel your pain mate,

Take out the plugs, connect them to the caps and lay them on the head so they're earthed.

Turn the bike on, stuck your thumb in a plug hole and kick the old girl over a few times.

You should get a big, fat blue spark that coincides with compression and you should smell fuel. If one of those three elements is missing then the bike won't go.

This is real rough-and-ready 'Bush mechanic' stuff but it should be enough to get you looking in the right direction (ignition/carburation/cam timing).

Backfiring normally points to an ignition problem but I don't want to give you any false leads. Start with basic stuff and you'll soon find the root of the problem(s).

And, for what it's worth, I love Mikunis!

Cheers!
Rudi