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James Lecy

2007 Yamaha yfz450 Idle Issue

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Doesnt want to idle unless choke is on and then it really high. Back fires constantly. Installed bigger jet because plug was really light. Could it be Timmy or bad carburetor?  Yamaha guru's help me out.

 

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Do you have a factory exhaust or aftermarket? 

* Added to the topic title -  your issue and manufacturer. 😁

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12 hours ago, James Lecy said:

Doesnt want to idle unless choke is on and then it really high. Back fires constantly. Installed bigger jet because plug was really light. Could it be Timmy or bad carburetor?  Yamaha guru's help me out.

 

It sounds like you have a low speed jet clogged up.  When the choke is used to keep a motor running it generally leads to the low speed idle circuit being stopped up in the carburetor.

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I've had pretty much this same issue on my 2003 Kodiak 450 for years.  It's really annoying when plowing snow given all the start-stopping-stalling.  At times I've used the choke slightly engaged to keep it running, but I know that's a band-aid fix.  I've tried messing with the idle speed, but that didn't really work.

Which jet is the low speed one?

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The carburetor would have to be removed from motor.  The carburetor would have to be disassembled soaked in a carburetor cleaner and the jets cleaned out. Air blowed through the passages in the carburetor. New parts added if needed and the carburetor reassembled and reinstalled on the motor. Repair manuals for that year, make and model should have pictures and written information on carburetor removal and repair.

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21 hours ago, James Lecy said:

Doesnt want to idle unless choke is on and then it really high. Back fires constantly. Installed bigger jet because plug was really light. Could it be Timmy or bad carburetor?  Yamaha guru's help me out.

 

Have you checked the valve adjustment . My 2008 did the same thing when I bought it brand new. Brought it back . The said it was old gas . Same problem . Would only start with choke on  even when warmed up . It would idle then back fire and stall. Adjusted valves . (To tight ) . Don’t need choke to start and idles fine . Worth checking .  

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