CRF150R jetting
  • Chemx
    Posts: 4
    Joined: Wed May 01, 2019 11:08 am

    CRF150R jetting

    by Chemx » Mon Jun 03, 2019 12:30 pm

    Hi all,

    Please bear with me, as I'm new to riding/maintaining dirt bikes, but I am soaking up all the knowledge I can.

    I live in northern NY. Weather has been great for riding: 60-80 degrees, although 90-100% humidity lately. I'm at ~300-600 ft elevation.
    I have a 2017 CRF2017R that has never started easily. It has always taken around 1/8 to 1/4 throttle to start with several kicks (cold) with the choke pulled out (closed? sorry if that's the opposite. I get confused. it is pulled out, though). On occasion when I get it started, I push the choke back in before taking off and it dies. If I start again 1 or 2 times it seems to work itself out. Starting hot has never been a problem. The rest of the power band (?) has had smooth acceleration with no issues. So after lots of research I decided to go from a stock 38 pilot jet to 42. Maybe I should have gotten a 40 but I mistakenly thought my current jet was a 40 already.

    Well I successfully (with the help of a mechanic friend) removed my carb, gave it a thorough cleaning, and replaced the 38 jet with the 42. It still starts very hard, but now if I get it started, it will sputter and die if it sits at idle.If I give it throttle, it will die also. After some time trying with choke off and on and lots of kicks, it will eventually stay on. It also seems to stay on in less time in this idle/dying stage on a 75 degree day with 90% humidity as opposed to a drier 65 degree day.

    Am I correct in interpreting that I may have gone from a too lean condition to a too rich condition? If this is the case, does that mean I should now mess with the amount of idle and/or the fuel screw? I assume the main and leak jets are fine and should remain as they are since my only issues are upon startup/idling. Please correct me if that's all very very wrong (or a little wrong!).


    Thanks in advance for your thoughts!
  • Leardriver
    Posts: 462
    Joined: Wed May 05, 2010 10:33 am

    Re: CRF150R jetting

    by Leardriver » Tue Jun 04, 2019 3:25 pm

    The 42 pilot will work. It is a little rich, but it only affects starting and idle. You may be trading easy starting for blubbery rich jetting after the bike is warmed up.

    Leak jet, (fad of the month) main jets, and accelerator pumps are all adjustable, but none of them affect starting, except for a completely blocked accel pump, which is used to squirt some raw fuel in for easier starting.

    Your 38 is the right pilot, and maybe yours was plugged. You want to judge driveability by how well it runs when warm. Driving off with the choke on when cold is just fine, we have all had bikes that needed it.
  • Aussiecrf230
    Posts: 1962
    Joined: Fri Jan 06, 2006 11:11 pm

    Re: CRF150R jetting

    by Aussiecrf230 » Tue Jun 04, 2019 4:46 pm

    Hi Chemx,
    Have you set the fuel screw to say 2 turns out and once warmed up adjusted to give even idling.
    If you only end up less than 1 turn out you may have to drop the idle jet still.
    If you end up more than 3 turns out it would suggest the idle jet is too small.
    Doubt this would be the fact in this case and would look for an air leak first off.

    Make sure you have a clean air cleaner that isn't over oiled before you start the process.
    Let us all know how you go.

    Assume motor is healthy in other respects and the valves are properly adjusted.
    Ray
    Australia

    CRF230F 2004
    C30F Power Up needle
    Mains 132
    Idle 45
    2 turns out
    Baffle out, Screens In

    It starts,it runs,it gets to where all CRFs can get to without the valve or valve plate dramas

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