My friends 400ex bogs when it hits high rmps in first gear nd low in 2nd gear. Then the throttle like pulls back. It doesnt have the same power.

 

Sounds like it might be time to clean out the carb or buy a rebuild kit. Possibly time for a new throttle cable.

 

try cleaning out the carb or some octane booster, maby the gas is no good or somthin.

 

You might as well drain the remaining gas out of the bike instead of wasting it on octane booster, which does nothing for the bike if it isn't set up to run premium. Regular octane is recommended. Use high octane if you have high compression only (12.5:1 or higher). The higher octane is simply resistance to pre-ignition, which causes engine knock. High octane gas can actually cause a carbon build-up on the spark plug, therefore lowering the performance of the bike, and menaing that spark plugs need to be replaced more frequently.

Try changing the spark plug anyway and get rid of all of the gas after you clean the carb out.