Need jetting help 2008 YZ450F

9 replies to this topic
  • gtxkid

Posted February 15, 2012 - 07:47 AM


I moved from Colorado to Florida and need to rejet.

Model: 2008 YZ450F
Edit Revision Date:
Main Jet:162 Now from Colorado 5000ft
Pilot Jet:48 Now from Colorado
Starter Jet: 72 Now
Leak Jet (if any):
Fuel screw/Setting: 2.5
Needle/Position: I think middle.
Filter: No Toil
Pipe/muffler: Dr D
Piston is 13:75:1
Altitude Range: Sea Leavel
Temp Range: 85
Humidity Range: By the Beach

I moved from Colorado to Florida.

Bike has a 13:75 to 1 piston in it with a DR. D pipe.

I am now at sea level.

  • grayracer513

Posted February 15, 2012 - 08:07 AM


You don't appear to be asking a question. Two days ago, you started this post:

I advised you to read through the '08 jetting listings to see if there was someone close to your situation who had posted the jetting they use. I take it that you don't feel like you found anything? Go back and read post number 1 in the '08 jetting thread. I know that bike, and it ran really well with that setup. If not that one, there are a number of sea level postings to use as examples.

The basics are that increasing altitude makes the bike richer because the jets stay the same size while the air gets less dense. A rough rule of thumb is to reduce the number size of the main and pilot jets by 1% for each 1000ft increase in altitude. So, for a 4000 ft increase, you reduce the jet size to .96 of what it was, making your #48 pilot a 46 (use a 45, since it's closest). Decreasing altitude is the opposite. For a 5000 ft drop in altitude, increase the jet size 5%. For example, 160 x 1.05 = 168.

  • gtxkid

Posted February 15, 2012 - 02:25 PM


Do you think the piston has anything to do with it.

  • grayracer513

Posted February 15, 2012 - 04:29 PM


Rarely. 13.75 isn't that much of a percentage increase over 12.5. But higher compression tends to enhance low speed manifold vacuum which in turn can increase the strength of the vacuum signal at the pilot jet. That can sometimes mean that you need a leaner jet to compensate, but a lot of times it evens itself out.

  • AquaNut

Posted February 15, 2012 - 05:03 PM


I live in Orlando, FL and after I installed my Yoshi exhaust, a local mechanic put my bike on the dyno. He went to 55 pilot jet, opened air screw 3 turns out and took the needle clip down one notch from stock. Bike runs like a champ!

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  • gtxkid

Posted February 18, 2012 - 05:02 PM


Thanks Guys
I am working on it.

Looking at the Zip tie mod.

  • Yamiryder

Posted February 18, 2012 - 05:30 PM


Looking at the Zip tie mod.

It's pretty simple and straight forward...

  • gtxkid

Posted February 19, 2012 - 09:51 AM



What Main jet did he use

  • gtxkid

Posted February 22, 2012 - 02:19 PM


I should get parts by this weekend i hope.
Still would like to know what size main jet Aquanut's mech. used.

  • gtxkid

Posted February 29, 2012 - 03:55 PM


Parts came today.

AquaNut Did you happen to find out What Main jet did he used.

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