'08 CRF450X - Help with jetting
  • neo__04
    Posts:5
    Joined:Tue Apr 14, 2009 3:22 am
    '08 CRF450X - Help with jetting

    by neo__04 » Tue Apr 14, 2009 4:08 am

    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 in advance
  • [email protected]
    Posts:5039
    Joined:Sun Aug 14, 2005 6:21 pm

    by [email protected] » Tue Apr 14, 2009 4:34 am

    -Get the 450X JD Jet kit.Check out it's reviews in the on-line store, it's been the best seller in the store for a long time. CrfsOnly ships to Australia,and they also have the excellent R&D or Crfsonly/Kouba fuel screw, you want one of them.
    -An NCVS needle along with a 165-170 main jet combined with a 45 pilot jet (or some even like the stock 42) with it has given satisfactory results to many guys as well.
    -Check out the 450X "stickies", there's a jetting data base so you can see what is being run that people are happy with.
    -You'll also see 'airbox mod'. It needs done, but not until the jetting is squared away. This is easy, and involves cutting along the lines Honda molded into the airbox to show you where to cut, or just opening up the side vents works well too, as in the JD kit instructions and in the 'How-To' section. Neither increases the bikes susceptibility to swallowing water in crossings regardless of what the uninformed may tell you.
    -Lose the emissions thingie, you'll never get rid of decel popping if you don't. The catalog has an excellent Applied unit to do the job, but you can do away with it by performing a modification to it ,and it'll look like it's stil there should you run into the Gestapo. Skoot 22 has a great "How-To" in the stickies with pictures in the 450X forum where he uses JB Weld to do a beautiful job.
    With the jetting fixed and airbox correction you will have a bike that runs smoother with easier to modulate power, starts quicker, runs cooler (more than you think) and has more power top to bottom as a bonus.
    These modifications work great with stock or after market exhausts. An opened exhaust will reqiuire only a main jet on the larger size of the range and maybe an 8th to a quarter further out for the fuel screw. Doug
  • Asmith
    Posts:14381
    Joined:Mon Apr 10, 2006 7:52 am

    by Asmith » Tue Apr 14, 2009 7:04 am

    Lot of good info there.

    I agree that you'll have a hard time dialing it in using the stock needle. Changing to either the JD red or the NCVS needle will help alot and allow the use of larger mains.

    The 70 that you removed is not the leak jet, it's the starter jet. The leak jet is in the bottom of the float bowl itself. Leave the starter alone, it's fine.

    Running either of the needles suggested with a 165 to a 170 main will get you in the neighborhood.

    A little fine tuning with the fuel screw after that will dial it all in.

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