I tend to agree with WD.  155 main seems extreme when you consider the stock is 145.  Going up 4 sizes in jets might be ok, but you'd want to get there 1 at a time.  I've got the stock pilot and main, and simply got rid of the white spacer, and my mpg dropped from mid 70's to high 50's (got 58 last tank.)  That's a pretty big drop, but my throttle response is soooo much better, that it's worth it to me.

"Ideal" air to fuel mixture is around 14.6:1, but an engine will "run" from about 11:1 on the "crazy rich side" all the way up to 18:1 on the "make your nose bleed lean side."  You're definitely better off at 15 or 16:1 than 12 or 13:1, so I'd err in that direction if at all.  My personal preference is 14:1 for "hot rod" applications, and 15:1 for "daily drivers."  I don't have my exel spreadsheet out right now, but I think a stock S-40 runs around 15 or 16:1.  Can anybody confirm or deny?

Rob did you notice the ceramic headers required a richer mixture?  I noticed when I wrapped my header with heat tape the bike acted like it was running leaner...

Not trying to hijack, trying to provide quick alternatives to test a leaner mixture since I thought we were pretty convinced we're dealing with an over-rich condition...

well I ran for a bit today, and it seems that the backfireing is worse. Also it seems to be at max RPM at about .5 to .75 turns out. is this odd.
    since the pebble ordeal, i cant help but wonder if it is related. So much work on the bike in so little time it makes me dizzy. I due for a 400+ ride this weekend and I am sure all my questions will find answers on the road.