What is the correct fuel mixture for a stock 2004 rm 250?

For a 250, you can get away with a leaner mix like 40:1 but I still race a 250 2-stroke from time to time for fun and I run 32:1. More oil = less friction, less heat, better sealing, etc...

Any idea what it was jetted to run? the difference between 40:1 and 32:1 is fairly minimal and if the bike is jetted fairly well I doubt you will tell a difference. If the plug is black it is too rich.

15:1 fuel air ratio is considered best in most applications. Too lean runs hot, too rich fouls.

32 to 1. That means 4 ounces of two stroke engine oil per gallon of gas. NEVER use motor oil.

If you have the stock valving, I would run 2.5w Motorex in the damper to compensate for the stiff feel stock, and thicker oil in the spring chamber such as Mobil1 5w20 to allow the oil lock ring to do its job on bottom-outs. I'm at 375ml in the spring chamber and I weight 155lb.

Exhaust Power valve setting for stock is: 1/2 turn out from closed. **3/4 of a turn for extra low-end grunt. [all varies depending on jetting selected,..start at stock 1/2 turn out ... and X-periment from there] .

Exhaust power valve adjustment for "stock setting" is: 1/2 turn out from closed.

http://www.bikebandit.com/suzuki-motorcycle-rmz250-2004/o/m6667

Here is a link to bike bandits carb page for the rmz. Looks like the stock pilot is 35 and the main is 168, it looks like there are two other jets too, starter and power.

the mixture may be too much one of two things you can do
1) switch to synthetic oil mix or
2) go to a hotter plug it will last a little longer but will still foul

my bike runs best 40:1 but you can run it 32;1

4 stroke engines require a leaner than normal fuel/air mixture to start when hot. The cold start choke allows more fuel into the mix. The hot start choke allows more air into the mix.