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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
YZ400F stumble at 5K RPM
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[QUOTE="Rich Rohrich, post: 1367420, member: 16241"] I never found the YZ4xxF engines difficult to tune, even when the power was well north of 50hp. I've had more practice at it than most, so I might not be a good point of reference. Without riding your bike I couldn't say for sure what your problem is, but it's pretty common for guys to put a pipe on a big 4t that causes a huge dip in the torque curve where the pipe is out of tune. This dip in the torque curve can really upset the fuel curve and flat spots are not an uncommon side effect. The stock Yamaha pipe and exhaust can are really good on these bikes. Just something to consider. [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
YZ400F stumble at 5K RPM
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