2008 YZ 450F Engine problems...Skipping 5th gear

I have had my bike for exactlly a year now and has ran great until last week i was out riding and was in 5th gear when it started to skip and cut out and lose power, it wont let me get to the top of 5th gear and makes a clicking noise... I tore it down and checked the valves and the carb, along with draining the tank and checking my clutches and basket everything was good to go but still experiecing the problem. It only happens in 5th gear about half throttle... Any advice or help?

Will it run alright at full throttle, or not take any more than half? Does it seem otherwise normal in all other gears?

When the skipping occurs, does it seem as if there is some mechanical part that will not hold the load, like the chain jumping teeth, or a gear skipping?

It wont run at full throttle alright it skips or cuts out from about mid to full... It is normal in all gears except 5th... It seems like a gear is skipping or something or maybe the bike wont hold the load... We changed the jets today and it still has the same problem...

It's not the engine, it's the transmission. The locking lugs on the sides of the 5th and 3rd pinion gears (on the main shaft) are rounded over to the point where instead of holding in gear under a load, the two are pushing away from each other against the shift fork, the lugs jumping from one slot to the next. The only fix for this is to replace the two gears. The shift fork will also have become bent by this, and will need replacement as well.

It's not the engine, it's the transmission. The locking lugs on the sides of the 5th and 3rd pinion gears (on the main shaft) are rounded over to the point where instead of holding in gear under a load, the two are pushing away from each other against the shift fork, the lugs jumping from one slot to the next. The only fix for this is to replace the two gears. The shift fork will also have become bent by this, and will need replacement as well.

How many hours would this repair take?

It involves a complete tear down. The cases have to be split. A pro could probably bang it out in 4 hours. In a home shop, it just depends.

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