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YFZ450 quad jetting help

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i hopefully should be getting my jets and exhaust in the mail today and was wondering the best possible jetting settings to run. just the basics

2005 Yamaha YFZ 450 quad

GYT-R aluminum exhaust

GYT-R exhaust header

GYT-R needle and jets (40 + 45 pilots, 155,160,165,168, and 170 mains)

K&N air filter with airbox lid removed

it comes stock with a 42 pilot and a 158 main. im thinking of running a 45 pilot, 165 main and the needle in either the 3rd or 4th clip position. does that sound close? should i adjust the air/fuel mixture too? if so... how many turns?

i live in northern cali with elevation ranges from sea level to 2000 feet. any help would be great! thanks!

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cool... sounds good enough. guess ill go a bit richer on the main. never hurts! hopefully this will work right the first time and i wont have to do anything else.

oh yeah... whats with that "taffy" mod i read bout one time for the FCR? does that just apply to the DRZ's that came with it or any/all FCR carbs? thanks.

my name is James too.. 😢

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45 pilot

1 3/4 turns out

middle clip position

#168 main jet

Have fun!

James

James,

I have an 04 YFZ 450 with less than a tank of gas thru it. Running stock pipe uncorked and airbox lid off I've tried the 42 and 45 PJ at every pilot screw setting from one to three turns out as well as the 3rd thru 5th clip position and 165, 168 and 170 MJ. Main problem is bad stumble/stutter at 1/8 to WOT as well as pop on deceleration.

Any ideas before I reinstall the baffle, airbox lid and stock jets/clip position and start again? Haven't touched anything else.

Sanks

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Sanks

The needle is the heart of the engine! What needle do you have?

Stock needle. Seems like too big a problem for jetting or needle, fouled plug maybe? When do you know when the plug is fouled?

Sanks again. (not my name, it's German for thank you)

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I should be getting my jet kit soon so could anyone give me any suggestions on the best settings?

YFZ450

HMF slip-on exhaust

removed airbox lid

and i should be doing the cam mod soon so count that too

Im in Southern New Hampshire and elevation is about 140 ft

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BlueDevil,

Follow the kit installation and setup instructions.

rep,

If nothing is working, pull the carburetor off and look into the carb from the engine side. The bottom of the slide should be flat and the hole in the slide should be closer to the bottom than the top. If the hole is near the top, then the slide plate is upside down.

James

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BlueDevil,

Follow the kit installation and setup instructions.

rep,

If nothing is working, pull the carburetor off and look into the carb from the engine side. The bottom of the slide should be flat and the hole in the slide should be closer to the bottom than the top. If the hole is near the top, then the slide plate is upside down.

James

James,

Are you saying it may have come from the factory upside down?

rep

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The plates occasionally have come from the factory upside down. It's been more common on the KTM's, but you never know if a mechanic might have been trying to cure one issue and created another.

I helped one rider solve this after 2 months of tuning with the plate upside-down. It was a shop mechanic who caused the problem to begin with.

James

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Fixed it by running with lights on. Heard about this?

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