The issue with your carb/bike is unlikely to be the pilot jet as this only affects the first 25% of throttle.
If the bike is starting easily it's probably the case the pilot jet is clean, but give it a quick once over.
If the problem you have is fuel related it will almost certainly be either a main jet issue, or needle jet.
Check here for settings, http://www.crm250.com/specs.asp

Mike

so i have to buy a 150 main jet?

crmgreece wrote:so i have to buy a 150 main jet?

What main jet is currently in the carb?
What exhaust system is on the bike, D.E.P. or standard?
Mike

All stock

What's the compression like?
Mike

for 2T engine it has much compression. and it works very smooth... but when it goes around the half RPM something holds it....

If it has primarily been used for commuting, it might require an exhaust de-coke, and repacking of the exhaust material.
Two strokes are beautifully simple in operation, UNTIL something goes wrong, then many faults masquerade themselves as something else, and only by elimination can the true fault be found.
The end can [ silencer] can be re-packed, and actually makes a huge difference to the power when done.
Mike

I try it with out the end can and does the same. I cant figure out if the main can of the exhaust is full of oil... how i will figure it out?

crmgreece wrote:I try it with out the end can and does the same. I cant figure out if the main can of the exhaust is full of oil... how i will figure it out?

The same way, take it off and either burn it out, or use caustic soda [ with extreme care] and dissolve out the oil. Oven cleaner fluid will also work, a propane burner will do the job, just suspend the pipe with one end open upwards, and direct the flame into the open lower end [ heat and flames rise].
You could run the engine with the exhaust removed [ don't upset your neighbours though] and check if the engine revs out, [ wear some ear defenders], you might be able to see if the power valve is actually raising with the increased revs, [ Wear goggles, or glasses as well.
Mike

Is there any possibility that the engine has a limiter? Mine does not wheelie with 1st or 2nd gear.

crmgreece wrote:Is there any possibility that the engine has a limiter? Mine does not wheelie with 1st or 2nd gear.

No, or least not as standard. Your bike seems to lack power, what final gearing is it running?
As I said trying to diagnose a fault on a 2T is always tricky, and from a thousand miles away somewhat harder.
Your sure the power valve is being activated? They suffer from carbon build up which stops them working.
Mike

Yes. when you move the PV with hand it opens and close. When i remove the exhaust and run the engine i can t see it because the gas hit me in the eyes

Run it with the exhaust on and take the cover off where the cables connect to the PV. You can watch it move as you rev then. You can also mark the extremes of movement of the PV arm and see how those translate to the actuation with the exhaust off and looking down the exhaust port. You may have to adjust the PV position according to the manual?

i do not have the manual. do you have a link?