YZ 125 Loss of High End Power - Yamaha Forums
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post #1 of 3 Old 02-09-2012, 02:57 AM Thread Starter
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YZ 125 Loss of High End Power

Hello all,

Let's first start off by saying i have a 2006 YZ 125, stock bore, stock pipe, FMF shorty, excel rims, Posey Motor (some shop that the previous owners had it freshened up by, still kept stock bore), BR1 suspension, etc....

I started loosing compression about a month ago, so i decided to rebuild the topend with a standard OEM 'D' piston (it was a wiseco before). After the rebuild it seems to have much more compression and runs great - one kick wonder. However, since the rebuilt i have had poor high end power. It almost seems like it doesn't want to hit the powerband anymore without flaking out. If i put it in second gear and hold the throttle wide open, i can hear the piston pinging a bit as well.

So i ripped it apart again, cleaned the power valves, checked my V-Force 3 reeds (one was chipped, so i bought brand new pedals), inspected the piston (all looks good), put fresh gas and premix in as well.

I even took the cylinder and piston to a shop to have them looked at by a professional and he said there's nothing wrong.

At this point i'm at a loss of what could possibly be the problem... Any info would be MUCH appreciated!

Thanks in advance fellas
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post #2 of 3 Old 02-13-2012, 12:45 AM Thread Starter
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Problem Solved.

After all that work. As well as cleaning the carb, and taking it to a shop for an inspection on the topend and powervavles... it was simply due to the exhaust silencer.

I took it off (temporarily - my neighbors hate me now) to see if it had been inhibiting my powerband from engaging, and sure enough... the bike was back to normal, as far as power goes (if not better due to all of the tuning I had done.
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post #3 of 3 Old 02-14-2012, 06:24 PM
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Sounds like you may be a tad rich on your main jet... I wouldn't run it too long without the Silencer... the length of that plays into the overall tuned length of the exhaust
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