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whipit1k

2003 YZ450 midrange stumble

11 posts in this topic

I have a totally stock 03 450- no mods, very low hrs. it stumbles like crazy in the midrange- no mods, low hrs, no clogged air filter, notyhing obvious. anyone had this problem? it acts rich but i just pulled the needle out just to be 1000% sure it was in the standard position- and it is. I am looking suspiciously at the TPS. anyone?

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Yeah I know that the jet most effectiong that part of the powerband is the needle, no problem. i have never seen a stock bike run so poorly with completely stock jetting, thats all. I was wondering what other potential problems could cause this. I am looking suspiciously at my TPS

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Why dont you just unplug the TPS and see if it helps. It will run fine without it. I doubt it is the TPS personally.

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My '03 does the same thing exactly. Black spark plug but missing and popping in mid-range like it's lean. I've ment to unplug the TPS to see if that is it but haven't gotten to it yet.

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Bro, I was just speaking from experience. Mine was doing the same thing. raised the needle...BRRRRRRRRRRRRRRRAAAAAAHHHHHPPPPPPPPPPPP

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I will try leaning the needle one position today. It just seems wierd that a stock bike in new shape would run so poorly with the stock jetting. If it is just the jetting, Yamaha really screwed the pooch on their baseline settings with this bike.

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These bikes are very sensitive to changes in weather and jetting. Sure everything is clean? Motochump was telling you he RAISED the needle, which will richen it not lean it out. Jetting is trial and error sometimes. Be patient you will be there soon.

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