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Discussion Starter · #1 ·
I recently took my bike's carburetor apart to clean and rebuild it. The problem I was (am) having is poor throttle response especially when going from low throttle opening to full throttle. I am fine getting it off idle and moving slowly. If I wack the throttle open it falls on it's face and then surges after it catches it breath. It is worse when the bike is cold and gets better when it warms up but never goes away. All the jets are clean and I can't find any damage to the vacuum slide assembly. If I pull the knob for the starter enriching valve it will rev fine throughout the rev range so I'm pretty sure it's a lean condition.

Do I understand correctly that the starter jet is part of the starter enriching circuit, the slow jet is for idle and small throttle openings, and the main jet is for mid-to-large throttle openings? I thought it may need a bigger jet but I have a 2003 TRX350FM that doesn't have this issue. I'm at less than 100 ft above sea level for reference. Anyone have any thoughts? Air leak in the vacuum piston maybe?
 

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Discussion Starter · #3 ·
No mods to the bikes. I've had them since 2005. The vacuum spring and the throttle stop spring look fine. I bought a brand new pilot screw assembly including the spring. The vacuum piston moves smoothly and drop back into position correctly when I move it with my finger. When I nail the throttle the piston bounces up and down rapidly before it finally gets pulled up and out of the way.
 

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Discussion Starter · #4 ·
Ok. Is there anyway to richen the mixture in the middle of the rev range? I don't know of any adjustments that can be made to this carb other than the pilot screw. Would it require a new slow jet or main jet?
 

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Pilot screw (and slow jet) controls Idle-1/4. The clip position on the needle controls fuel from about 1/8th throttle to about 3/4 throttle, main jet from just below 3/4 up to WOT.

If your machine is stock, I would clean the carb really well, set everything to stock specs and see how it runs. You may need to invest in a rebuild kit. Without mods there is no reason to have to start adjusting things, stock should work perfectly fine.
 

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Discussion Starter · #6 ·
I've gotten the carb as clean as I can get it. And it is loaded with o-rings from a rebuild kit. New OEM pilot screw. Haven't wanted to try the QuadBoss jets though. Oddly the kit doesn't come with the needle jet or needle jet holder.
 

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I've gotten the carb as clean as I can get it. And it is loaded with o-rings from a rebuild kit. New OEM pilot screw. Haven't wanted to try the QuadBoss jets though. Oddly the kit doesn't come with the needle jet or needle jet holder.
most kits come with everything cept the float, and rubber plug. where is the main jet needle seat ?, I don't see it in the bottom of last pic ??.
 
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