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Been riding a 88 Honda TRX250R and last week picked up a 08 YFZ450 in very good condition for $2k. The guy lost his job unfortunately so he sold it for a good price. It has been sitting for a year, had gas in it already and have ran it close to empty until it was starving for gas and back firing and filled it up with new 91 gas.

She runs pretty strong other than the blimp of the throttle and it'll almost die (sometimes it will) and i did the zip tie mod and it didn't improve it at all. I noticed even after she's warmed up that on my TT track on straight aways I run through the gears all the way up to 5th full throttle. on every gear near the top end it sputters, cuts out some until I shift and does the same at the top end of the RPMs. Anyone have this issue?

I have a friend that is a Yamaha dealer mechanic and he mentioned that we need to go through the carb. I told him about a Boyesen quick shot and the Sparks TPS bypass and he said to never bypass the switch as it will make it hard to start and that the quick shot is a waste of money. He's a busy guy so I don't rely on him a lot to fix my quad issues but he has done some work on my 250R.
 

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It could be your jetting, need to know what is the current jetting, what mods and elevation.
 

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It could be your jetting, need to know what is the current jetting, what mods and elevation.
Sorry completely forgot about that part. Current jetting as far as I know is stock. Mods is a full exhaust sparks with slip-on and a pro flow intake with K&N. I'm in central oklahoma, 100 degree temps and elevation is 892ft
 

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Sorry completely forgot about that part. Current jetting as far as I know is stock. Mods is a full exhaust sparks with slip-on and a pro flow intake with K&N. I'm in central oklahoma, 100 degree temps and elevation is 892ft
if your jetting is stock with all those mods then that's your problem and its running lean. Although one question, how do you have a full exhaust sparks system with slip on?
 

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I have the same exact problem, i have a 2005 yfz 450 I just purchased... its bogging or like sputtering out when I hit high rpms in any gear until I shift... I've tried every jet setting, even the air fuel ratio and still the same i thought maybe its dirty and still after a cleaning I get the same thing... i swapped the carb with my buddys carb we know is running 100% and it ran perfect, I put mine in it again and same thing so i know it has to do with the carb, please help....
 
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