250-500cc wr250 lacking power

hey guys looking for some help here. I recently got a 04 wr250 for a great price but needs a little tlc. It starts up first kick and runs good, but doesnt seem to have the power it should. it does not have the top end snap i think it should. Its all stock except vforce reeds. Ive gone through the basic...clean card repacked silencer, check power valve opperation, reeds look good. Did a compression test, its at 160psi. Jetting is at 400 main and 35 pilot with a #4 slide. Its the mikuni TMX carb. Looking for some recommendations, appreciate any help i can get.

I would put a new piston in for starters, if it still has the original it could self destruct at any time. The stock compression ratio is low, I had my head modified for more compression, my engine now reads 180-190 PSI. That will help the low/midrange power. The FMF Gnarly and Powercore silencer work really well on this motor, especially if you're looking for more top end.

Does it flatten out on the top? My 09 WR 250 in stock form would rip in the mid but go flat on top (it did this more if I richened the main). After switching to the Gnarly pipe I was able to jet it richer on the main and it revved out way better + it smoothed out the mid without taking anything away.

Agreed. Safe mechanicals (new piston) then head mod is number one.

Repack the silencer, change the plug, check the power valve, if it is sticking it will make it loose top, Mine would stick open and would loose bottom until it would go back, I was using Castor 927 and seemed to gum up the power valve. I new a few guys that went a lot of hours on a piston, I doubt it is a stock piston, take the exhaust off and look up in the cylinder, you can see the piston and check for wear. My 07 with the stock pipe and silencer would still pull up top with the same jetting

Take off cover and check power valve. I was having same prob and found out that the little plastic control arm was broken. $5 part, easy to put back. Problem solved n

New top end! My bike tested out at 205 psi with a year on it. I would change it at 180 psi.160 is to low.

ok i didnt want to but ill look into i new top end. didnt want too put much money into it but seems like the right thing to do. This is my first husky, is there anything i should about doing a top end as a posed to a jap bike? landydoug yes it does flatten out at the top end with strong mid, decent low end. Thanks guys

Di you check power valve. It may be sticking, or disconnected. Those bolts rattle off the post sometimes.

yes i checked the power valve. Everything is functioning

Bummer. I was hoping that it was something simple and cheap. I don't have the Mikuni carb, so I dont know if those jetting spec's are good. Either way a new top end is going to be nice. It will run for a long time. Good luck and keep us posted with how it comes along

thanks for the responses guys. I was hoping it was the power valve but i took the lef cover off and it was moving freely and seemed to be opening all the way when revved a little less than half throttle (on the stand in neutral.) Then took the right hand side off and same thing looked good, was not gummed up too much. I'm thinking it may be time for a new top end. I'm just worried if a do a top end and it still is where its at ill be pissed! haha. Im more than capable of doing it i just dont want this bike to be a money pit. As far as pistons pro-x seems to be the cheapest but should i just go for the wiseco? Thanks again.

alright so i got borrowed my buddies compression tester and it read 210psi consistently... glad i didnt get the parts for a new top end. Dont buy a comp tester on ebay. so now my question is where am i losing the power? should i switch out the carb? different jetting? i dont know where to start, i thought it was the top end but pleasantly surprised when i saw 210psi. Any thoughts?

Take your muffler off and see if it makes a differance.If it does your silencer needs to be repacked.

What is your current jetting? As I said above I had to go lean on the main to get the stock pipe to rev out. (390-400) Now that I have a gnarly pipe I'm using a 430 main and it rips all the way through. If you really like top end power I've heard that the Pro Circuit pipe gives it even more top end.

It has a 400 main jet and 35 pilot, the silencer has been repacked. i'll try a couple diff jets and look into a new pipe. thanks again