Speaking of going richer, I was curious about changes that should be made when you go from standard piston to first oversize. If the bike seems to run good still with no changes its it still a good idea, as a matter of practice, to make any immediate jetting changes. I'll see if there is anything in the tuning literature in the tech library and will search the forum as well. Just a random question as I prepare to go meet a buddy for a beer. I'm off!

I'm thinking surging is 4 stroking hence rich, so if you go richer it can only make matters worse. I guess there's could be two types of surging as in "Lean Surge" [starving for fuel] where it would fade & need more throttle to get over it. Or Rich mixture 'at that possition' which still means more throttle to get over it, but would blubber or 4 stroke in old terms.
Firing while slowing down on a closed throttle [annoying] is different again but i'm thinking you mean at a steady throttle cruising in your case.

In my mind (!) surging is a lean condition and sounds like a slower nnnyyyuuuuunnn...nnnnyyyyuuuunnn...
You can feel this if you turn off the petcock and ride around gently before the engine dies.

Four stroking is a rich condition and sounds like a faster duh duh duh duh duh duh. 
You can feel this if you leave the choke on too long.

Maybe I should make some audio recordings so we can all have a good laugh!