Lack of power at high rpm??? HELP

[AbusedBigRed]

Hello, I got a 1986 Big Red 250ES and i was riding it few hours ago then sundently it lost all his power, It's still running fine at low rpm but when i rev it up it take alot of time to reach higher rpm and doesnt have any power, Im pretty sure it's fuel filtrer but my dad's think it's carburator so please help me
BTW: Where is located the fuel filtrer on those machine?

[torque]

there is a fuel filter in the sediment bowl in the fuel shut off valve

[AbusedBigRed]

there is a fuel filter in the sediment bowl in the fuel shut off valve

But what do you think it is?? Fuel Filtrer or the carburetor

[big red in iowa]

It's starving for gas in the upper rpms, it's a process of elimination, start at the tank and work towards the carb...when you find the problem tell us.

[Thorpe]

carb... Primary nozzle or main jet is likely plugged... Good time to rebuild the carb. (rebuild, not just clean IMO)

[AbusedBigRed]

Well my carb had a rebuild 1 month ago and it was running fine after it

[torque]

it will take ya 2 mins to pull the filter out and clean it. what does the inside of the tank look like. if it is full of rust could be your problem. just some simple advice.

[dustrunner]

i have a 250es with a rusty tank but i run a in-line filter and havent had any problems... after cleaning the carb , so i would reccomend the same...

[AbusedBigRed]

So far now i have checked the air filter, The fuel filter, Changed the spark plug but i still have this problem but few hours ago i had a discution with the local atv dealer and he told me that he already seen that problem, The thing is that the cover of the spark plug ( That i dont know the name in english ) Must be at his end of life, So this cause a bad fire, I'll change that tomorrow and tell you about it!

[AbusedBigRed]

Finaly found the trouble! The screw that hold the carburetor piston was missing , So the piston was now able to go up !