Question about 2010 Yamaha WR250F
What do you recommend for the jet for trail and motocross style riding, i already have a FMF powercore on it! Do you thing i should open the airbox as well
I recommend that you don't open the air box unless you put a bigger jet in it because if your ratios arent right you will blow it up real quick
Posted on Feb 20, 2013
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Posted on Jan 02, 2017
SOURCE: i have a 98 yz125,
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"
Posted on Apr 06, 2011
Hard to give accurate info with out seeing the bike with jetting but I would suggest take a reading from the fuel air screw
if the bike running better with the fuel air screw in carbi at 2.5 turns out or more then definitely increase pilot jet up 1 or 2 sizes if you get the bike to run well between one - two turns out on the fuel air screw that is where your jetting should be
I wouldn't be concerned with main jet at all - it should be fine for wide open throttle unless you feeling power loss when you open it right up
also if you are getting backfire or popping when de accelleration that also hints toward lean pilot so a size or two change in pilot jet would be worth trying
Posted on May 25, 2011
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