08 Honda cr450r powercore 4 and megabomb header jetting advice
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Thu Dec 03, 2020 12:45 pm

    Here is the wifes 400EX jetting.
    MJ=170
    Needle clip one position down from std. setting.
    That was jetting for 500 ft. elevation and sand dune running.
    I should have went one size larger PJ in it but it's such a PITA to work on that I left it OEM pilot and 3 turns out on the fuel screw.

    You asked about the fuel screw. [ air screw on 2 strokes ]. On four stroke FCR carbs [ and CVK models ] the in [ CW ] direction reduces fuel for cold starting and idle to just off idle running. It does have influence throughout the zero to full throttle but just off idle it becomes very minimal. Adjusting out [ CCW ] enriches the starting and idle to off idle condition.
    Most standard settings are 2 1/2 out from lightly seated. That is a baseline.
    Going in or out until you feel a slight acceleration in RPM's and a smoother idle is a base way to try to get a good point. If you are having cold starts that take longer than normal cranking or longer than should be to warm up try adjusting the fuel screw out [ CCW ].
    If you have to go more than 3 turns out to get proper fueling and starting that is indication to move to the next larger PJ.

    For reference, 2 stroke carbs are the opposite effects and control air going to the primary system. In direction will reduce air, out increase air.

    Hope that helps.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Wed Dec 09, 2020 5:58 pm

    Hey, so I finally got a little time to install. I went with a 182 main jet, 45 pilot and went 4 down from top. It was around 45-50 degrees. I used the hot start lever to help tune the af screw. It’s wild because I never really looked into it, so didn’t know the engine should rev up. Even stock, my cr450 , yz450 and yz250 never made any noticeable changes when pulled, so I always figured it was a wasteful lever.
    I also noticed my head pipe didn’t glow red when idling and revving standing still, which was never the case.
    I don’t know maybe I’m crazy but I think this was a good idea. Throttle response was instant, as long as I take out the slight play in neutral throttle position before whacking it.
    If I DONT take out play in throttle and wack it, I hear a loud pop/backfire and engine dies instantly. Riding down block, everything felt good up to 2/3 throttle . No backfiring. I wasn’t able to get a nice WOT run so not sure If going 2 sizes up from stock was a good idea. My logic was that I’d rather go on the larger side, and know that I need to go down, than just go one size up, and not be sure if the 2nd size up would be even better. Plus, at wot, I figured it’s better to be on the richer side anyway, no?
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Wed Dec 09, 2020 6:01 pm

    Also, I plan to go 1 size up on pilot and main, and go one notch down on needle for 400ex with yoshi slip on. It seems like that’s in line with what you did. Only thing is, without having a hot start lever, how do I tune the AF screw and be sure I have the right size pilot?
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Thu Dec 10, 2020 6:57 am

    You can adjust the fuel screw by listening to the idle speeds. You can also use a vacuum gauge to monitor as you adjust but I usually only do that on street bike multi carb bikes.
    You can also tell when you have it right by the way it starts.
    If you are not going to change the PJ from the OEM , you will be out to the end of the adjust range of the fuel screw [3ish turns CCW] that's ok just don't go past the 3 CCW as the screw will not have much left of the threads holding it.
    Give it a try & see how it goes.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Thu Dec 10, 2020 11:42 am

    On the 400ex, I’m going one size up on pilot jet, one size up on main jet and one clip position down from stock. So I’m basically going one notch richer on all aspects.
    On the cr450, I went one pilot size up, one needle clip position down (richer) and two main jet sizes up.

    What was odd when adjusting fuel screw on the 450 is that I was unable to notice any difference in idle when turning it in or out. I know the sweet spot is supposed to be when the idle speed peaks, but really didn’t notice it. Luckily, the hot start lever trick worked well.
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Thu Dec 10, 2020 2:57 pm

    The reason you did not notice much difference is due to the larger size PJ. It's only when they are under sized and on the lean side do you hear a very noticeable difference.

    Glad you got it all figured out - Good job. Make notes and log them in your service manual. Later if you try to recall stuff like that it's easy to forget what you did exactly when someone asks - Or at least that's the way it is for me. :lol:
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Aftershock00
    Posts: 11
    Joined: Sun Nov 29, 2020 6:46 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Aftershock00 » Sun Dec 20, 2020 5:17 pm

    Hey, so I finally went to jet the 400x carb. Took me 4 damn hours. Granted it was my first time disassembling body parts of quad and messing with this design carb. I went up to 40 pilot and one size up on main jet. My gut is telling me I should have went up two sizes on main just because it was such a pita, I’d rather be slightly rich and deal with it than be lean and have to go through that again.

    I bothered getting to the needle only to find out it is not an adjustable needle. Wtf??? What do I do? I was so sick of wasting the day that I reassembled it all. The pilot is def the right size, starts right up at half choke no throttle. I didn’t have a chance to ride it. What am I supposed to do about this needle that has only one clip position?!?
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 08 Honda cr450r powercore 4 and megabomb header jetting advice

    by Back2-2 » Mon Dec 21, 2020 7:32 am

    Yes- Honda really screwed that engineering design all to hell. Major PITA...

    You have two choices on the needle. Research a similar taper needle that has the clip & slots from other bikes or ATV's or use small shim washers to lift the needle in increments.
    I would try it like it is. It is a very forgiving engine and unless you are going for top perfection you will probably be ok. Two steps on the MJ would compensate for some of the mid range fueling that a higher needle [ lifted ] setting would have given you.

    Try it and see what it feels like the way you have it right now and go from there.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200

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