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Do I need to re-jet?

This is a discussion on Do I need to re-jet? within the Yamaha YFZ450/450R (2004-Present) forums, part of the Performance /Technical category; I have a 05 YFZ 450 and want to know if I take out the spark arrester do I need to re-jet my quad?...


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Old 05-22-2010, 03:39 PM   #1
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unhappy Do I need to re-jet?

I have a 05 YFZ 450 and want to know if I take out the spark arrester do I need to re-jet my quad?
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Old 05-22-2010, 06:21 PM   #2
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yes. it needs to be re-jetted in stock form... they are lean to begin with.
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Old 05-24-2010, 01:57 PM   #3
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Yes, you will need to bump the main a few sizes up, then go ride and test and see how it feels.
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Old 05-24-2010, 03:20 PM   #4
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remember, these machines need a certain balance of gas and air, if there is not enough gas in the mix, they are called lean, if there is too much gas, they are called rich.

the jets are what effect how much gas is put into the engine.

ANY time you change something on the quad that effects how much gas or air it uses, you need to consider whether the jets are still ok, and re-jet if needed.

a new air filter will let more air in, but not gas...
a new exhaust will let both air and gas through faster, and will require more gas for the mix.
etc etc... so the stock bike is lean, if you change anything, it will need to be adjusted.
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Old 05-24-2010, 04:34 PM   #5
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Agreed!
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Old 06-20-2010, 12:58 PM   #6
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bowtie, im running 160 main and 40 pilot...what changes should i make to up to the cinders in flag? i just got it back from rudy at dfr...dyno test and tune...its running amazing. but i need to rejet for cinders...HELP
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Old 06-21-2010, 02:38 PM   #7
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Wow a 40 pilot and 160 main??? seems very thin with that much motor. I am running a 48 pilot and a 180 main on a DFR build that has a FCI intake, Venom exhaust, and 12.5 slug and I am slightly rich. I would take a 42, 45 pilot and a 158, 162, and 165 mains with you, and just let it be for now. If it seems off, rejet while up there.
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