problem with 250ex stumbling

[d33pt]

It seems to run ok up to about 3/4 throttle where it cuts out and sounds like it's backfiring or stumbling. At this point, it stops pulling, just kinda flattens out. Power is normal up to that point. This happens in every gear and you can even hear it in neutral, but of course it's more apparent in the lower gears when you're riding.

I've replaced the plug (which looked normal when i pulled it), and cleaned and oiled the air filter (which was also pretty clean when i pulled it). I didn't change anything on the bike to cause this and it ran fine a month ago. it's just a stock bike except for a unifilter that i put in because the stock filters are junk. mine tore apart at the rubber boot.

[Aceman]

I would try cleaning your carb out taking a good look at your mainjet making sure nothing is plugging the hole. Blow it out with air or carb cleaner don't stick anything in the hole to clean it out. If it's clean you could try going up or down a couple sizes on the mainjet to try and solve the problem.

[d33pt]

I tried cleaning out the carb really well...also went up on the main jet size from the stock size of 95, i went up to a 98, then a 100. it didn't make a difference at all. i was really hoping that was the case because it makes perfect sense. any other ideas guys?