250-500cc Brand new 2010 WR250 got loud and bogs down low

It didn't start out that way. The first time I rode it, just to break it in, it was snowy so it was hard to tell how it ran, but it seemed strong. The second time I rode it, yesterday, I got on it once I warmed it up and was in awe at the broad powerband that pulled hard from the bottom all the way to the top. It was amazing! But about halfway through my 2-3 hour ride, the bike seemed to get louder and I didn't have the same low end power, instead it bogged up to about halfway through the rev range when it came on the pipe and took off.

What the heck happened? It sounds almost like a bike with old packing in the muffler, with the increase in noise coming from the silencer, rather than an expansion chamber leak, but it's not really louder when it's on the pipe. I tried tuning the air screw but I could not restore it to its original form. I didn't really crash and I couldn't find anywhere the exhaust was damaged or leaking. Anyone else had this happen? I want it back the way it was! Help, please!

I had similar symptoms on my 09 but each time it would go back to normal after 20-30 seconds. I checked the PV adjustment under the left side cover and the bolt for the opening limit was loose. It hasn't happened since I tightened it. I'm not 100% sure, but I think my PV was opening too far and sticking open.

I pulled the pv cover off and all the fasteners seemed tight, and i ran it today and watched it open and close. I was thinking pv because my old kdx had similar symptoms and I spent forever messing with the exhaust, and then found out the powervalve was loose and stuck open.

The weird thing is that it seemed like it was running ok this morning. I didn't take a good ride on it but it sounded quieter and didn't seem to bog, although it could be my imagination. I wonder if the powervalve sticks when it's hot? That is the first thing I'm gonna look at if this happens again.

Your main jet has either fallen out or it is loose.

Why would you say that?

Well, it is just a hunch, sometimes we look to complicate things, anyway it's an easy check. I had the same thing on an earlier 250cc and that's what it was.

Well, it would seem the bike is fine and has sorted itself out. Maybe I was just imagining the problem. It ran strong all saturday and the suspension broke in about halfway through the ride and felt fantastic.

I got a very similar problem,

2010 WR250, feels like its going to go into the power band but just boggs,, been through every adjustment possible in the carb,, no luck - really am a 100% positive now its not the carb causing this
(today I took it to a buddy that works on a local motocross team and he went through the carb all over again also same problem - very confused about what he thoght was the problem - magneto he says is not producing enough power - need a race mag installed,, looked this up and husky only has one part number, no diffrence between the enduro or motocross version 250 or 300)

Bike has about 1.6 hours on it "Brand New" -- spent that long so far trying to figure out its problem,
Never gave it a thinking to try it out the box due to all the restriction it had, removed all that first before i gave it a start up...

What I have done,
Removed the restristion (restriced expansion chamber, air filter plastic cover, throttle stop)
Rejetted the carb (carb power kit included in the crate) and installed a procircuit silencer.
The sparke on the plug looks good when kicked,, at high rpm's under load??? gap is good - plug is good

Been reading on the power valve and starting to think this could be it as the power valve starts opening around 6,200rpms (as per the book says?) so this is about where I can feel the bike starts to get its power and it just dies right off...

Anybody else have issues on new out the box 2010 WR250's????

If it starts pulling hard at wide open and then dies off it could be running the bowl dry or pulling a piece of trash up that covers the main jet, then you let out and the bowl refills or the trash falls back in the bowl. The bowl going dry happens more in the higher gears at wide open throttle. I would at least pull the carb bowl and have a look. Also what jetting are you running? (just curious)

Got the bike all going today,
The low power fault was my own fault,, I would not have found it unless I read a few things on this fourm one being a guy had a power valve where the mechancial stop was all the way down,
I checked this and removed the expansion chamber to look in the barrel (as shown in the 2008 WR service manuel)
While the expansion chamber was off I had an idea to compare the weight of the 2 expanison chambers I have,, detailes below,,

I have a Procircuit silencer and as this pipe does not fit the stock expension chamber I hacked up the emmsisions expansion chamber (had the mesh insert knocked out first and the small pipe cut off and brazed up) since I knew the expansion chamber would get banged up anyway no point to just throw away the emmisions pipe,, better modify it and use it first,,, seems as this is where I fuzed up!

Last weekend i spent a good 6-8 hours trying things on the carb,,, this is why yesterday I took it to my friends shop,, since they could not figure it out I spend yesterday night here on the net and this morning messing around on the bike,,

What was found is the emmsions pipe has another evil secret inside --- a small orrifice inside that cant be seen without a flashlight and cant be knocked out easily, while comparing the weight of each expansion chamber by holding in each hand the emmsions pipe was still heaveir even the mesh knocked out of it

I installed on the 2nd fully open expansion chamber that came with the bike (not cut yet to accept the pro-circuit slincer) and installed the stock 3km long silencer,, started her up and WOW,, just the diffrence in the sound I knew I was on the right track..

Took it for a quick run around and the power was there but not qiute right yet but its coming online,,
Put it back on the stand and rejetted it the way I had it before taking it to the shop,,
Needle Jet 35
Main 380
Needle 3rd clip
Scewed about 1 1/8 turn out

Lessons learned ----
1# The factory emmissions expansion pipe needs to be hearled against the wall into the garbage can upon bike delivery,,
2# Dont trust what half you buddies say is wrong with the bike -- Find it yourself and learn (I am now a carb installation and removal expert -- 5 min jet & needle check no problem)
3# The factory Michelin enduro 140/80 tire will be burned and a 110/100 installed this week

Power? This bike you need to hold on!!! I am just at 215 pounds and damn 1st, 2nd, 3rd can lift the front no problem !!!

Plans for the future -- My TE250 is not good enough after feeling this 2banging power -- 300cc bore kit for the TE to be ordered soon (the TE is my trail bike - the WR has been converted from enduro to motocross)

I have a 2009 WR 250 and had similar issues. I have the upgraded Keihin with the JD jetting done for my area of riding (Pacific Northwes). I am running the stock pipe and silencer. I noticed the bike would build power well from idle to mid-range and then sign off as though it hit a wall. I took the bike in and had it looked at and they were suspect of the carbeurator. I took it to a 24 hr race and it still ran the same. I removed the left side cover for the power valve to see if it was functioning. The shop told me to start the bike and as you work the throttle you should see the power valve mechanism open and close. The main bolt holding the assembly was backed out all the way and was not holding the fork in position to open or close the valve. I snugged it up and now it runs like it did day 1. The shop said they have had several people have this issue and reccomended some locktite on that bolt.

My '09 WR300 was bogging when it was just coming on to the pipe, then it would sputter and I would wind up short shifting because it would not pull through cleanly. Checked for the rag in the airbox, cleaned the air filter, checked the packing in the silencer, checked the reeds everything was fine. Pulled out the stock plug it was worn, the gap was huge, tossed in a B8EGV... Bam! back on the pipe and pulling like a freight train. and it starts easier too.