125-200cc WR 144 sputtering in the higher rpm range

Hello guys, I've got a problem with my 2010 Husky WR 144 (Mikuni Tmx 38 carb) . The bike keeps sputtering in the higher rpms, no matter what main jet I'm running. In winter I usually ride a 480 main jet. I tried out the jets all down to 450, but the problem stayed exactly the same. I've also installed a new airfilter, cleaned the whole carburator and installed a new spark plug. Has anyone got an idea what the problem could be? I'm thankful for every help. And you may excuse my english because I'm german..

And something else I noticed: After a few seconds of sputtering the bike revs out and has it's regular power, so the engine itself should be okay... But after letting off the throttle and getting back on it, the problem occurs again.

make sure you have an "R" or resistor plug

Then remove the tank and check your wiring, especially the ground.

beste

What about reeds??

Could it be something as simple as a bad plug? I have had one foul and do stuff along those lines

I had the same issue and the cure was leaning out my power valve.It feels like it's not getting enough fuel when in reality it's opposite.

I'm sorry for not replying for so long, my profile wasn't enabled until now, and i hadn't noticed..
Thanks for the replies, I'm gonna check all these things!

Could you explain that a bit more? How can you lean it out?

So: I've got a correct spark plug, checked all the wiring and cleaned the contacts, tried a new spark wire and cleaned out the power valve. No changes so far.. My last hope is "leaning out the powervalve" as Idacurt mentioned. Could anyone explain this? And I'll be checking my reeds as soon as the special tool arrives..

I have a lectron , power valve has a adjusting screw.On other standard carbs you would go leaner on the main jet.