I run 30:1, so I just mix up jerry cans with 15 litres of fuel and half a litre of oil... Others are running 25:1 up to 45:1 I think so it depends on what you feel is a safe mix... _________________ NSR300R - Why did i ever have a 250...
No that should be fine as it's only a slightly higher ratio than I'm using, and you could probably go as high as 50-60:1 if you're jetting wasn't too extreme. but don't quote me on that! _________________ NSR300R - Why did i ever have a 250...
pretty much any oil can be used for pre-mix. It's the other way around you need to watch out for. One of the things you need to remeber is that the oil is heavier then the fuel, so it will settle after time. When I leave pre-mix in over night or more, I tend the shake the bike around prior to starting it to mix the oil and the gas as much as possible again. _________________ Charles Gallant
For road use I would avoid 40:1 and 50:1 mixes.
Crossers use those sort of mixes but they are rarely on full throttle for long - point and squirt. So if all your riding is in town then ok.
However, if you ring its neck on the open road and have the throttle pinned for a while then go 30:1 as a minimum. It will be a bit smokey in town but....
I have heard that for the Manx and TT people run 25:1 as the bikes are on throttle for so long.
Oil is cheaper than pistons, barrels and bodywork + your arse
One of the things you need to remeber is that the oil is heavier then the fuel, so it will settle after time. When I leave pre-mix in over night or more, I tend the shake the bike around prior to starting it to mix the oil and the gas as much as possible again.
I have tested Belray 7SI in a bottle in my apartment and no separation happened after a month.
I had 20liter cans with premixed( I think its TTS) gas standing for half a year in my garage and no separation occurs.
As I've seen old gasolin, without mix go bad, I usually put the old unused premix from last year in the car and give the NSR fresh gas, but I can't see any separation happening. _________________ Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom
It all gets compllicated when you change the ratio, as you actually affect the fuel going in and can run the bike lean woth too much oil, so it siezes anyway! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
when you figure the difference between 30:1 and 35:1 it is so small your jetting won't make a difference. Were talking amounts that the small jump in jet sizes won't even make a difference. _________________ Charles Gallant
Right or wrong I always run 40 or 50:1 at the track. My MX bike runs great like that. Only one seizure ever on the NSR and I'm pretty sure when some one read a main wrong and installed a main 2 sizes lean that might have been the problem. I think thats what all those white spots on top of the piston were. Good point Dave I was thinking the same. Charles do you know the math on oil to fuel versus fuel to air? I try jetting for temp. with my oil ratio _________________ 1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike
Jetting for temp is only part of the equation. You really want to jet for air density. Temp is one of the factors that determines the air density, as is humidity.
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).
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
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I think thats what all those white spots on top of the piston were. 
Good point Dave I was thinking the same. Charles do you know the math on oil to fuel versus fuel to air? I try jetting for temp. with my oil ratio 