09 YZ450f bog?

I have an 09 450 that's has a bog on landing that's been slowly getting worse and yesterday became so bad that you cannot ride the bike anymore as I almost went over the bars

I've ridden and raced yamaha's for 8 years so i usually can figure most problems out but this one has got me guessing.

Jetting is one bigger on the pilot & main, 48 and 165 main which were changed this spring to get rid of a slight bog and the bike ran great all summer to fall until the last 2-3 weeks now. located in MN.

I noticed this bog a few weeks ago and checked the valve clearances and found three valves on the tight side so reshimmed but still the bog is there on landing. it's not a split second bog, it looses power until you completely let off and get back on it. 1-2 seconds at times.

I'm gonna go through the carb tonight and see if i can find anything but figured i'd check to see if anyone has had this problem.

Any input would be great.


good idea see if anything is in the carb. i would take the carb off and clean out the bowl and make sure there is nothing broken it it. i had a quad that did that but i cleaned out the carb and it runs great now. you might need to adjust the jetting. just a suggestion

Check float level too

second the float level. Lower it if anything as most YZFs are set a bit high from the factory.

You never mentioned your fuel screw setting, make sure it is around 2 turns out. Those things have even been known to fall out.

and it is 3...the float level is off

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