'08 CRF450X - Help with jetting

Hey all,

Just doin some work on the bike and trying to get the carbie all set up.

Bike was stock, cut the baffle out of the exhaust, going to cut the airbox as well, just after some advice with the jetting, I'm a complete noob.. so go easy.. And im not really in the position to just buy a JD jetting kit.. so rather buy the 1 or 2 jets i need.

I took the carbie apart tonight to check the jets, i dont know which is called which, but you guys will know... the middle jet was a 145 (main im assuming), the jet directly above it was a 45 (assuming pilot) and the jet below to the left of the main was a 70 (assuming leak?)

I live on the coast of Australia, so close to sea level, so base altitute on sea level to 1000ft or so. Does it make much difference? (e.g. will be very close to what i listed.. but could be up to 2000ft.. no idea really)

Can anyone with some experience give me some advice on which jet sizes to start with, i havent adjusted the mixture from stock, so it bogs a bit and likes to be nice and warm before running nice from takeoff.

Also is it worth buying a new adjustable fuel mixture screw for it?

Thx heaps for the help

First off don't cut your air-box open until you re-jet as you will be running real lean if you do. I found that at 80 to 90 degrees my 2008 ran fine at sea level to 1000 ft.( Caribbean ) completely stock so your temps may be cooler in Auz , hence the bog when cold.

There was a real nice jetting thread on here but I can't find it now ,the other guys will recommend to change your needle jet to a stock CRF 450 R needle ( sorry don't have ref no.) and either a 165 or 170 main jet , stock is 145 as you mentioned . I did not have to change my 45 pilot jet and to be honest if you are sticking to just sea level to 1000ft you may not need to put in an adjustable fuel screw only if your elevation and temps change alot.

If you put on an aftermarket exhaust with open air-box the 170 main will be required but with just the cut stock exhaust and air-box opened the 165 should be fine.

I just ordered an end cap for my stock exhaust from DB Dirt Bike Pty in Auz as I could not find one in the US , a little pricey , hope to have it by tomorrow , they are at 02 4872 4222 seem like real enthusiasts .

Have fun and welcome to the site

Nick ( Barbados)

Just found some old threads and the needle is called up as an NCVS , not sure if this will mean anything to your Honda dealer but it is a CRF 450 R needle and is what most of the threads say works best if you do not go with a JD Jetting Red needle.

It`s cheaper.

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