Help w/ Jetting 2003 YZ450F

5 replies to this topic
  • tmonteton

Posted May 01, 2005 - 05:13 PM


Ok guys, i really need some big time help on dialing in the jetting. I just did up the motor with some porting and polishing, wiseco high compression piston, hot cam stage 2, Titanium Valves / Springs, and boyesen quick shot. Problem is that it has a terrible bog @ about 1/4+ throttle, its almost un-ridable !! After the bog, its fine. Its not the basic bog that we are accustomed to either, its definitely with the jetting im thinking at this point. Ive tried several variations except changing the leak jet but non have made it spot on at this point. here is the current jetting -
Main - 170
Pilot - 48
Needle @ 3rd clip
Fuel Screw - 2 turns out
Everything else stock settings
Im in Sacramento @ sea level
if anyone has info on my set up - PLEASE HELP

  • walent215

Posted May 01, 2005 - 05:18 PM


too fat on the pilot try 42

  • yzf450jack

Posted May 01, 2005 - 06:08 PM


Sounds like your too rich your dumping to much fuel and it can't burn it off that's why it bogs go with stock jets and put clip at 5 and see how it runs There's no leak jet on your yz so you can't change that :naughty: When I went 470 it liked smaller jets :naughty:

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  • tmonteton

Posted May 01, 2005 - 06:34 PM


? No leak jet ?? Maybe im referring to it differently - I had assumed that I had a "leak jet" so to speak within the excelerator pump - the exc. pump screw to be exact, as it would seem that it is squirting in a specified amount of fuel ?

  • yzf450jack

Posted May 01, 2005 - 06:56 PM


No leak jet I looked 03 yz 450 don't have one there is a spot were it would go but no hole :naughty: The WR has one :naughty:

  • SureBlue

Posted May 01, 2005 - 08:21 PM


With your mods I don't think going back to stock jetting is right. Keep what you have but start with the needle on clip 4, then clip 5. Set the fuel screw to 1,5 turns and keep it there when trying the needle. When you find the correct clip position, finally fine-adjust the fuel screw.
You may need to change the needle to NCVP, then start at clip 3.
You did not tell us the jetting and mods you had before when it ran fine.

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