Got a 2006 KX250 with a Pro Circuit pipe and muffler and Boyesen pro series reeds when under full throttle and under load such as going uphill it sort of breaks down and the plug sometimes fouls got the needle 3rd clip from top and standard main jet.Any help appreciated.

there is two ways to mount mufflers on small engines. one with two bolts through the muffler to the block or threaded to it. if you don't see bolt heads then you unscrew the whole muffler.

A Hayward S180T sand filter holds 150# of sand. In other words, fill the filter 3/4 full of sand (to the point where the tank starts to round off). Make sure, however, that you fill the tank 1/2 full of water first. This will help to cushion the laterals and prevent them from breaking from the weight of the sand. Make sure to cover the hole in the top of the lateral assembly pipe with a cup or duct tape to prevent sand from going into the pipe. If sand gets into the pipe, it will come out into the pool. Don't forget to remove the cup or tape after adding the sand!

I would first make sure the power valve is decarboned and moves smoothly. Jetting is trial and error as so many things can affect the mix. Temp. humidity, gas quality, oil ratio etc. Tht being said you can make small changes and keeping a log with results. First write down baseline settings. Include main jet and pilot jet numbers found stamped on the jets and needle number. You don't say where it is you are trying to get power. 125s have poor bottom mid power, it is all on top for racing. Don't change and race or you may keep going when you should stop and melt something. Try to test at the altitude where you will race and read the plug often, cleaning or changing the plug between tests. Be alert for the surging feel of lean mix with racing idle do not let this continue. Remember 0 to 1/4 throttle, pilot and needle base width. 1/4 to 1/2 throttle controlled by needle mid taper. 1/2 to 3/4 throttle needle tip and main. 3/4 to full is the main jet. Find out the stock settings and make sure to start near there. I don't know about a spes pipe but pro circuit has charts for jetting and maybe a support line. I really feel you will get more from a clean powervalve, repack the silencer, clean airfilter and maybe v-force reed. Gearing can offer some options. I just read about a James Dean jet kit for cr250 that puts more power in the low mid. I might try that for my bike. Good luck, just remeber " too lean, too long- too bad"

If this machine has a spark arrestor in the muffler this may be blocked, check around the muffler outlet for a gauze which may have carboned up.You need to find out if it is running rich, or lean which is causing the problem. too rich a fuel/oil mixture will also cause the machine to bog down at full revs, it should run a 50-1 mix with good quaility two stroke oil. If it is running too lean it will also cause this type of problem ( blocked fuel filter, cracked fuel hose, dirt in the carb )

Check the fuel filter, air cleaner, and muffler for plugging. Check the fuel lines for decay or other damage. Make sure the carburetor is solidly mounted to the engine. Hope this helps!

mess in with the engine will need a carb rejet the only way to fine out what the right jetting is needed is to run the bike on a rolling road and test how much power its engine is putting out under full load,,and to fine out what its power band is now,,,thats if its has one now?? ,so you see its not just a big game of bunging on a bit here and a bit there and saying iv have sooped up me bike as it will now be a lot slower than it was before you toyed with it,,and buy the way you also need to change the air filter as well,,,now you may see were all that money go's when your racing bikes,,,1000, of bucks for only half a second off the track laps! if you realy wont to go faster,,,
get a biger bike!

a power blade will do good also a k&n airfilters rejett the carbs to the next size up so if its 155-160 boyesen reeds and a bigger front sprocket and a smaller rear thats about it buddy

Try reinstalling software. You may go to Control Panel, Add Remove Programs and click on Repair or insert CD and click on Setup

now then, i have a kickstart, i bought it for my kx 125 1999 but it doesnt fit it you send me the dimentions of the bolt it fits on to and the one i have will fit ill sell you it

For more power you can port the engine but I would start with performance Reeds. Also would adjust suspention and revalve if needed. That would be it for me…,,