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  • Carb jetting

    hey guys I know this is a common issue and I’m pretty sure I’ve seen it answered somewhere but I can’t seem to find it. When I bought my bike it was bone stock and I added pipes. The service guy told me to change the main jet and put a spacer under the needle and I would be fine. I get a cough off idle and have quite a bit of black on the inside of my pipes. I also ported the manifold and added a k&n stock replacement filter. Should I change the pilot jet?

  • #2
    I would. Go to a 37.5 Mikuni Pilot and add a second shim under the clip with the fat spacer and shim already there.
    See if that helps. Stacking shims under the clip with a stock needle, is experimenting, but if you’re patient, you’ll get there. You may end up adding another shim or two before you feel it’s right.

    By by the way, assuming it is still there, pull the rubber noise boot out of the bottom of the stock air box right where the air goes in. It’ll take a few bends out of the airflow, and increase the opening size.
    The plastic back of the air box fits into a groove in the boot. Think of a rubber grommet in a hole.

    Also, make sure the idle is set close to 900 rpms on a hot motor. Don’t mess with it after getting it set.

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    • #3
      Cool thank you. Im so glad you guys are here. By the way I think that your front fender mount is badass

      Comment


      • SKWEARpeg
        SKWEARpeg commented
        Editing a comment
        Thanks. It was a sink or swim thing, and it turned out pretty good.

    • #4
      So for an update on this I tried the 37.5 pilot and it seemed to be running really rich so I went back to stock. I did the poor mans bak and added a barons needle. I have the pms at 2 1/4 turns out. I still have a off idle hesitation. Any suggestions

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      • #5
        Put the 37.5 back in.
        What groove is the clip on the needle in?
        Are the fat plastic spacer and single washer(shim) still under the clip?

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        • #6
          4th groove and yes the plastic spacer and a metal shin are under it. It still seems to be running rich right off idle but I’ll try the jet again

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          • #7
            You can leave the shim out, and just put the fat spacer under the clip. That will lean the transition by a half step. You should be fine with the 37.5 Pilot though.
            What’s the history on the needle and seat(float valve) in the carb now?

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            • #8
              It’s been in since I got the bike. I tore the bowl and have only switched out the jets.

              Comment


              • #9
                Originally posted by fanaticx View Post
                It’s been in since I got the bike. I tore the bowl and have only switched out the jets.
                Since you’re in there mucking around anyway, I think I’d replace it. If it is original, it is more then likely responsible for a possible rich mix.

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                • #10
                  Ok. I’ll try and pick one up tomorrow since it’s been raining here and I have nothing better to do.

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                  • #11
                    Be gentle, and don’t mangle the float. If you use some small amount of care, you’ll be fine.

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                    • #12
                      I’ve rebuilt quite a few carbs I’ve just never had to tune them. Most are just lawn tractors and a few boats. The barons needle makes a giant difference in riding

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                      • #13
                        while your in deep. Pull out the float needle housing and replace the O-ring. ( if you have not done so all ready )







                        This space intentionally left blank

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                        • SKWEARpeg
                          SKWEARpeg commented
                          Editing a comment
                          If he buys an OEM set, the new oring should be on bottom of the seat half of the float valve.

                      • #14
                        Lets go right back to the basics. I read this thread and don't see the info needed to properly advise you on your jetting. What main jet do you have and what jet kit are you using? It sounds like if you were bone stock that the advice from the dealer was to shim the OEM needle. If that is the case you need to buy a jet kit to get it right. If you have an adjustable needle it would be nice to know what brand kit it come from and as I said what main jet you are using.

                        Comment


                        • SKWEARpeg
                          SKWEARpeg commented
                          Editing a comment
                          He ended up with a Barons needle in the 4th. The Main is still a mystery. He thought the 37.5 was to rich. Not sure why, other then his opinion, and the bike is a 2001, and the needle and seat age is suspect.

                      • #15
                        Something else came to mind while I was typing. Make sure your idle is set properly to 900rpms, on a hot motor. That in itself, will cause an off idle stumble, if it has been turned way down to where the bike will still run, but lopes like it has a cam.

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                        • #16
                          The main is a 167.5 and the idle is probably close to the 900. It’s not loping. I thought it was running rich with the 37.5 pilot because when you would open the throttle hard it was stumbling and running very poorly. If you slowly opened it it would take off a little smoother but the performance was way off.

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                          • #17
                            Also I called the only dealer that is open today and they have to order the needle and seat. Does anyone know the part number off hand

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                            • #18
                              5UH-14107-20-00 Needle valve set

                              Comment


                              • #19
                                Originally posted by fanaticx View Post
                                The main is a 167.5 and the idle is probably close to the 900. It’s not loping. I thought it was running rich with the 37.5 pilot because when you would open the throttle hard it was stumbling and running very poorly. If you slowly opened it it would take off a little smoother but the performance was way off.
                                If you are positive you have a Barons needle and have the clip in the 4th groove down from the flat end with a plastic spacer and 1 silver washer, 167.5 main jet,37.5 pilot jet with the pms at 2 1/4 - 2 1/2 turns out, you have the correct jetting for a 1600. If all of this is correct and the carb was cleaned then you need to start looking for an air leak at the intake manifold to carb joint or intake to head joint.

                                Comment


                                • #20
                                  So here’s an update and a big thank you to all that helped. I tore her down again today and followed the instructions to a T! Holy crap 4250 comes way to quick now in first gear! Apparently all the issue was the stock needle. I guess that’s what I get for trying to go cheap. Once again I appreciate the help and patience!

                                  Comment

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