Need jetting help 2008 YZ450F

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.

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.


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

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.

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!

Thanks Guys

I am working on it.

Looking at the Zip tie mod.

Looking at the Zip tie mod.

It's pretty simple and straight forward...


What Main jet did he use

I should get parts by this weekend i hope.

Still would like to know what size main jet Aquanut's mech. used.


Parts came today.

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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now