"flat Top End?"

[EXe3]

Hey,all hows it goin?.I have a question about a 2000 model Scrambler 400 2-stroke 4x4.I traded a 97 model,and a little boot for it not long ago,and now it has a problem (simple,I hope) It ran fine when I got it,but now it seems like when you hold down the gas feed throttle,it does good until it reaches a certain rpm,then just flattens out,and runs
rough with a noticeable power loss.I changed plugs,and that didnt help.I rode it a little a few days ago,and it ran ok,then it started just kinda fading out,until it finally just quit.I took the gas line loose at the filter,and it is getting plenty of gas through the filter. I let it set for about a week ,then fired it up,and there aain,it ran fine to a certain rpm,then "flattened out" again. Im wondering if there is maybe trash in the carb? Seems to me like when it set awhile,the trash may have settled in the bowl,allowing me to fire it up and ride it home,then got stirred up again,enough to cause rough running.Any input wold be appreciated. I hate tearing into it, if someone knows another cause to this problem. Thanks,EXe3

My guess would be dirt in the carb, maybe a clogged air filter. How many hours on it, approx?

[EXe3]

Hello.thanks for your opinion.Ill look at these things,and let you know the diagnosis.As for how many hours are on it,I dont have a clue,but the guy I got it from bored it 25 or 30 over,put in a little larger piston,and also installed a racing clutch,so I would guess it has relatively few hours on it.He also put wheelie bars on it,to keep bad things from happening.

[Mudstock]

Sounds like the air filter.
I clean and lube mine every 5 rides. Which really isnt enough for where I ride.
But that sound like the symptom. Could be carb, But think you have an airflow problem for sure

[kninja]

I'd have to say it sounds like your variator belt is either slipping
or your variator is not pressing hard
due to wear and tear on its bearings and spacers