250-500cc Losing power after getting on the pipe

Well that wasnt it.... Now its worse & doing it when I am powering up hills now too...... I just dont know what to do.......

Take you silencer off and go ride.Sounds like maybe it is plugged and needs to be repacked.

Have you taken off the left side power valve cover to make sure everything is ok there? Maybe run it with the left side cover off to make sure the PV is working properly?

not with it off but using the wrench it seems fine to me as I let it go but I will try that out just in case. I am taking it apart anyway tonight. Someone thought it might be that my carb is pre ignighting?? as I was riding back and forth past him. the problem is that i cannot test it out just reving up the engine. Seems fine that way and not till I ride the bike and I cannot do that in my neighborhood either.

if the problem is under heavy load and after about 5-10 seconds of full throttle look for a blockage of the exhaust, if your WR has a spark arrestor I would look there first

I second the power valve, because of the sound you are hearing. I had a 2001 Honda CR250 do it and it just needed to be cleaned. My WR started doing it last race and I cleaned it, and it doesnt seem to be doing it now. Kawi KDX's were known for that also.

could have a blocked intake in the venturi of the carb you know the two little ones that are on the intake side occasionally they can gum up with oil. carb clean the entire unit while your there

then I guess I didnt clean the PV all the way I guess then. time for the head to come off once again... crap...

My wr125 also has symptoms like this,usually when I'm pulling a long hill and it's on the pipe it will start cutting out when I'm up there in the rpm's,when I blip the throttle it will come back on and then start missing again when I hit high rpm's again, It has done this for years with three different carbs and now the lectron so I don't think it's the float level and my PV is clean and tight??
Could this be a CDI issue?

If I am reading all this correctly, I am still thinking power valve because after your last cleaning and tightening of that bolt you said it got worse, right? I feel for ya!!!

I think i found the issue. Small tear/hole in the Union from the reed cage to carb boot. I think it was sucking air and almost seized the engine so finding out tonight.

Power valve is sticking.

Whille working on my 08 wr250 I installed my clutch cover and somehow pushed the pin out of the top of the power valve assembly.It was gutless,but with the side cover off and running on stand it gave the appearance of functioning somewhat properly.It would still move but not quite as much as it should have.Found the pin on the magnetic drain plug.Make sure all your pieces are in place.