04' YZ450F Carby Problem


My brother has a 04' YZ450F the same as mine. He's been having trouble with his carby. After riding it for 15 -20 mins the carby gets stuck open part way (idles really high) and if it stalls its a dog to start (its a bit of a dog to start even cold). When he taps on the side of the carby it fixes the problem temporarily. He's had a new needle and seet put in it and it still does the same thing. He reckons he's going to rebuild the carby. Does anyone have any other suggestions before we attempt to do that?

Any other suggestions would be greatly appreciated.

If the slide were physically sticking, he could simply force it closed at the grip. What it sounds like is a lean idle condition. Start by looking for air leaks, like a loose carb isolator sleeve. If you find none, adjust the fuel screw to get the idle mixture right. If this fails to correct the problem, then you need to check your valve clearance before going further. A tight intake valve can cause this problem, and must be ruled out or you're just banging your head on a wall. :banghead:

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