This is as far as I've gotten on this topic:
About ECU Bumping:
http://rswarrior.com/forums/t/48956.aspx
Because over time we have learned different bikes have had different factory air:fuel settings in
the ECU when new, it seems likely air:fuel is individually adjusted at the factory. Before making
any changes to ECU settings you need to record and save the original factory setting. Further,
over time, be aware that someone before you may have 'bumped' the ECU air:fuel (you should ask).
For this reason a good place to record air:fuel ECU bump factory settings is the Owner's manual.
Its generally accepted that air:fuel ECU bumps must be up-or-down the same 'number' both jugs.
If you bump cylinder1 two points up, you should do the same to cyliner2 to maintain the spread.
Additionally, it seems confirmed the ECU Bump affects only idle, but not above-idle rpm range,
although there are also members who have made engine and exhaust mods and have run as much as
three years only bumping the ECU, without a Power Commander (or similar). This is all murky
and I've been unable to get information from Yamaha or Mitsubishi (the ECU manufacturer).
If you are considering a bump, do a search of this forum and read all posts since Jan 2008.
Also:
http://rswarrior.com/search/SearchResults.aspx?q=pistons+AND+userid%3a4686&o=Relevance
Edited: sorry I should have added this link too, and there aretwo more similar topic links I need to locate and insert herewhen time allows. My belief from reading the service manual isan ecu bump modifies air:fuel from the new baseline CO#'s at idle and across the rpm range. However I have never had my air:fuel adjusted via ecu bump while on the dynotuner as two or three members have - and nobody has directly answered their questions keeping in mind they are not claiming to be experts and they have personal info that doesn't match with what a lot of us think must be true.I find this interesting enough to bring their thinking forward because we value their contribution and maybe there will be an answer that makes sense.
http://rswarrior.com/forums/t/118282.aspx