What water to coolant ratio for yz250 2 strke do I use

That is determined by the coolant.
Some is already to go.
Or concentrate is 50 / 50, so half coolant and half water.

Coolant container should say "concentrate" or "do not dilute"

Best mix is 50 water and 50 ethylene glycol (coolant) Measure both of these in ounce or ml containers and add the same amount of each one.

The coolant bottle is under the hood and is labelled. A 50/50 mix of water/coolant is recommended. DO NOT take radiator cap off unless car is cold . HOT coolant will burn skin deep it takes a lot of water to remove from skin.

You should always use a coolant-water mix. Not only does it give you more protection fron freezing temps but it also gives you more protection from heat. Coolant added to water raises the boiling point.
Normally, cars and trucks use a 50-50 mix of water and coolant which is fine for most situations.Any pre-mix coolant is this ratio. Pre-mix does cost a little more but also saves you the hassle of doing your own mixing. You do have to watch if you are doing your own mixing because coolant is toxic. It's sweet smell will attract pets to drink and it can kill them. It does take more than a drop or two but it can so if you spill wipe it up.
Pure coolant jugs will have a label on the back that gives you a ratio of water to coolant based on temperatures. Read across to find an average low or high temperature in your area and read down to see what the recommended coolant to water mix is.
You should also pay attention to type. Coolant comes in 2 colors, green and red(or a version of it). Green is for cast iron engines and red is for engines with aluminum. According to those who know the green stuff will corrode aluminum and therefore the red is designed to be aluminum friendly. Using the wrong coolant could void warranty.
Hope this helps.

that is called the recovery tank and the level should not go down, if u keep seeing the tanks level drop then u have a coolant leak in the system, when u do top the system off ALWAYS USE 50%

if its full strenght 50/50

You don't really need to flush it out. Most of the time it's a 50/50 coolant/water ratio. Check the bottles - often coolant is sold pre-diluted so you can just dump it in. If not, mix it equally with water and add it until it reaches the full mark (or the top of the radiator) and you're good.

The typical ratio is 50/50 coolant to water. Make sure though that the coolant you bought is the concentrate undiluted type. Coolant comes 50/50 diluted as well, so you would not add water to this...

Mix at 50/ 50 for best result and protection will give -30degC freeze protection

Coolant=Antifreeze. It's the same stuff. It lowers your freezing point and raises your boiling point. That way you don't freeze your engine and you don't boil it when it gets hots. Now, onward....

The easiest thing to do is go buy 50/50 premixed antifreeze. The ratio is ready to be poured right in. The parts store will be able to tell which antifreeze will work best for your Jeep. It more than likely just uses plain jane green antifreeze. That's what I put in mine.

Otherwise you can buy non-diluted antifreeze and add water to make a 50/50 ratio.

A 50/50 ratio is important because too little antifreeze is bad, and so is too much. For instance, a system ratio of 80% is highly ineffecient. That's why I'm suggesting the prediluted stuff. A ratio too low risks having your block freeze up and bust.

If you do add water, DO NOT use regular tap water. Only use DISTILLED WATER. It's cheap, and it's free from impurities, whereas tap water is good to drink, but it bad for your antifreeze system balance due to extra minerals, etc in that water.

You can buy distilled water at any grocery store. It'll be labeled distilled, not drinking, water.

Your coolant should be changed every 2 years unless you have extended life coolant.

Be sure to check for leaks so make sure you're not loosing too much antifreeze. The tank where you pour it is called the reservoir tank, or expansion tank. It's where the coolant goes when it expands when heated.

Be sure not to let animals near the antifreeze. It has a sweet smell to them, but it's deadly. Antifreeze can be recycled. But if you must dispose of it, carry it to your local hazardous waste facility. It only take a small portion of that stuff to taint thousands of gallons of water.

If you have a 4.0 six cylinder especially, be sure to follow these directions. The blocks and heads are iron and they will rust really quick internally with too little antifreeze is used. These are awesome engines often getting 200k miles+.