03 WR450 jetting, bogs, etc.

I am totally new to the TT forum so help me if you can. I just purchased a used 2003 WR450 with 110 miles and need some guidance and updates. The original owner told me it was completely stock. He had an aftermarket pipe on it for a while (brand unknown) and removed it before he sold it to me. It has stock exhaust now except I installed a Yamaha GYT-R exhaust insert to replace the stock insert. The problem I am having is a persistent hesitation in the throttle, sometimes coming from an idle up to 1/4 throttle and sometimes from 1/4 up to 1/2 throttle. At full speed the bike rips, although I am going to remove the 150 stock MJ and install the extra 155 that came with the bike to compensate the increased flow in the exhaust. I have read about the airbox mods, etc and plan to do them but I don't think this is my problem from idle to 1/2 throttle. Another thing I noticed was after revved it sometimes will idle high before it returns to normal idle, similar to opening the choke. I asked the original owner about it and he told me it had not been ridden since last year and it ran fine then. :confused:If anyone has any suggestions for a starting point on jetting, etc I would greatly appreciate it.

JD jetting kit from the TT store will help a ton. If you still have hesitation issues then adjust you Accelerator pump on the side of your carb. :)

Might want to try adjusting the fuel screw that is located at the front of the fuel bowl. Especially since your symptoms seem to be at 1/4 to 1/2 throttle. You access the screw from the bottom of the carb. See pics here fuel screw and look here pilot circuit for instructions on how to adjust, look under "jetting the pilot circuit."

I have an 04 WR450 currently and I have just worked out the jetting on it. I too run with a stock airbox, stock pipe and GYTR insert. I am 4700 feet and only ride higher than that. See my sig for my jetting specifics.

I am not 100% sure about this since I have an '04, but a 150MJ seems on the small side for a '03 450. Stock for mine is a 165MJ.

What altitude do you run at? Does wide open throttle seem OK? below 1/2 throttle is mostly dictated by the pilot circuit and the needle circuit. I would also post this on the jetting forum if you have not already done so.

I have an 03WR, stock exh/airbox, uncorked her, removed the screen from the filter cage, and cut the gray wire. My jetting, for 2500' is 162MJ, 48PJ, DWR(04WR)needle, 70SJ, Zip Ty fuel screw at 1.25 turns....you DON'T need any jetting kit, I spent ~25 bucks for the needle and jets, 1/3 the price of the JD kit! She runs GREAT, a little rich with the GYT-R insert, perfect without it. :)

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