I use a weather station for temp and humidity, as well as an air density gauge to determine my jetting. I also never would do 2 steps at a time, I only do one step at a time. Of course my main jets range is much smaller (I think I have four that I use so there are no wild swings for me to take).
There are some good articles out there for jetting (on top of Andy's stuff on NSR-WORLD.com in the tuning section). I like Eric Gorr's stuff as well as HRC has some good articles out there (I turned some of HRC's articles into PDF format).
Eric Gorr's article on carb tuning
http://www.eric-gorr.com/techarticles/carbtuning.html
HRC's Articles:
Basic concept of Power Jets
http://www.nsr250.net/HRC_tech_notes/HRC_basic_concept_of_power_jets.pdf
Functions of Carb Parts
http://www.nsr250.net/HRC_tech_notes/HRC_functions_of_carburetor_parts.pdf
RS250 Carb Settings
http://www.nsr250.net/HRC_tech_notes/HRC_RS250R%20carburetor%20setting.pdf
Settings According to Seasonal Conditions
http://www.nsr250.net/HRC_tech_notes/HRC_Settings%20according%20to%20seasonal%20conditions.pdf
I tend to take good notes of all my sessions. I log temp, humidity, air density, weather conditions, time of day, tape on radiator, any jetting changes made fuel put in the tank. When I come in, I then log the avg temp of the coolant while I was out there, how many miles I did, how much fuel was used and notes about how the bike ran.
This way I have a complete history of what is done to my bike and I can go back to those notes to get a good idea of where I should be for jetting based on history.
Oh and if you are using things like weather stations and air density gauges, understand that the readings from one gauge can differ from another gauge. So try to stay consistent and use one set of gauges all the time.
I run the same fuel (VP C12) as well as the same oil (Silkolene Pro2+) at the same ration 25:1. This way I have constant factors to work with all the time. I drain my tank each night, I clean my carbs each day (complete tear down clean), I check my cylinders after each session (do a visual inspection through the exhaust port), I check my plugs after each session.
The next step for me is to hook up my det counter so I can use that for jetting and not use just the outside conditions as my guide (the det counter will tell me what's going on inside the engine).
as for the oil/fuel ratio and how it changes your jetting. I look at it like this. You have a gallon of fuel. What percentage of that gallon of fuel will be oil when mixed? couple % maybe? if you are going to change your jetting, you should change it only the % that the fuel has been offset by the oil. So lets say it's 2%, and you run a 165 main. Your next step would be a 168. a 2% increase of 165 would be 3.3 (about). This could move you up one jet size to the 168. But going from 30:1 ratio to a 25:1 isn't going to be the same increase, so I wouldn't worry about changing your jetting for a change that small.
Now when you are going from oil injector stock setup on an NSR (which has I think a 128 main jet) to pre-mix you may want to think about this. Of course by that point your also probably going with a modified intake, as well as after market exhaust. So your pre-mix is going to be the least of your concerns. Your modified intake will make a larger issue on your jetting at that point.
Okay. I will stop rambling about stuff I don't have a firm grasp on
All I know is what I have practiced has worked for me. _________________
Charles Gallant