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Mike’s XS pwk carbs

Discussion in 'The Garage' started by WelderDave, Aug 14, 2019 at 3:11 PM.

  1. WelderDave

    WelderDave XS400 Addict

    So there’s not a lot of info about these carbs on here, most of it is in the 650 forum, so I’m gonna write some stuff up in mine. Bear with me, I’m learning as I go with carbs, got everything down pretty well though.

    First off, it’s a good kit, I recommend a non vacuum petcock with a 90’ elbow and a T splitter all available on their site as well and don’t come in the kit.
    Tuning is a bit different. Here goes.
    Bought the 650 kit by mistake, but they are exactly the same except the jets.
    650 comes with:
    35 pilot, 120 main

    400 comes with:
    30 pilot, 105 main

    Main issue experienced with 650 and the 400 is the jets coinciding with the kit. Had to jump up a pilot and main jet size for myself as well as others with 650’s so the jets are a tad lean out of the box (also depends on your engine and altitude). I’ve got 35 pilot and 110 main (however I suspect I need a 115, but I won’t know until I get a chance to really ride it)
    All my maintenance is up to snuff, points, valve clearance, etc. just to note.
    All that is good and easy to figure out, do your pilot jet and main jets first because this is where it gets hairy. These kits come with the same needle profiles! Not good. You can get your jets right and drive it fine and all, but the midrange off-idle is rich and bogs the engine and can kill it if you snap the throttle. The profiles are off with both kits. ( I’ve compensated a bit for this by raising the clip and increased idle so it’s not so bad, but it only covers up the initial problem). I did some more digging, and found someone who diagnosed this issue and landed on jjm needle to really get it.
    Currently, I don’t have time at the moment to check the needle profile to let you know what comes with the carbs, but I will be doing so at some point very soon. I want a starting point before buying needles, and I’m trying to get into contact with the guy from the 650 forum that has it figured out so I can see how things pan out. I’m assuming profiles will be similar as the jetting isn’t to far off.

    I’ll keep everyone posted as I make progress, I figure it will come in handy when someone else is looking or is just “dealing” with how they are like I have been until I got fed up. I want throttle response and smooth performance.
    Last edited: Aug 14, 2019 at 3:41 PM
    BBS360 and Dan like this.
  2. Dan

    Dan XS400 Enthusiast

    Thanks for info. Intrigued as been looking at these carbs too. Interested to see how you progress....good luck
  3. WelderDave

    WelderDave XS400 Addict

    So the 650 forum when they synced theirs, they must have had an older kit that added a spacer for the intake boot to mount on farther away from the head, so they could still sync there’s the regular way, fortunate for them. The only thing I could do was even put the throttle cables and eyeball the slides to make sure they were just loose enough not to leave much slack in the throttle, and even so the slides opened and bottomed out at the same time. If you’re careful you can get it pretty darn good because you can hear when the slides bottom out and see it to make sure it’s lined up pretty damn close.

    The other thing I did was I screwed the idle adjustment screw all the way in and 10.5 turns out on each carb, then I warmed it up and adjusted my air screw 1 turn out from fully seated. Voila. You want to make sure they reach wot and close at the same time and a little bit of slack in the throttle cable to make sure it’s not hung up a little on one carb or the other.

    Last but not least I was studying the charts for needles on jetsrus and I finally figured it out and what others were buying, they do in fact, have jjm listed in a separate table. There are others, the 650 people have tried jjk, and jjl, the one guy ended on jjm as his golden nugget. Good to know for me, and when I get home I will check to see if my original needle has a part number to give me a starting point, I don’t wanna break out the caliper if I don’t have to, but I will if need be.

    So far, she idles great, wot I still think I may need a 115. One test I need to do is to check if I have a nice hard pull from 1/4 throttle to half throttle because that changes what you’ll be looking for in the needle taper. If it’s bogging and needs less gas from that pull I need a thicker bottom end of the needle, if it pulls good, I can keep the same. It appears the only thing the 659’s has to change was the top diameter portion of the needle, which is what controls the 1/8 to 1/4 portion of the throttle. Length and taper controls the 1/4 to 1/2 and then your main jet picks up the rest.

    To be continued...
  4. WelderDave

    WelderDave XS400 Addict

    Here’s what I found with the needle that comes with these kits. 2.6 mm diameter top end, and the length is 57mm. Part number was less than helpful it’s pretty worn, but with all the measurements I took with my calipers, it uses characteristics of a larger carb and the length of a smaller carb, and I couldn’t find any that matched up even close. I’m thinking this is a custom made needle.

    So I went on their website to see if they sold replacement needles and I couldn’t find any, but what I did find were 2 different needle jets. One is called main jet holder with its part number, and another is called an emulsion tube with a different part number, 2 different prices also. So I emailed them about it asking if one is for the 400 and the other for 650 and which ones for which. Waiting to hear back tomorrow. However my line of thinking is they can get away with using the same needle if they compensate for it in the needle jet.
    Wit that said, I also want to mention if you have one or get one of these kits, always pull the bowls off and make sure your plunger is clear, mine leaked first till I cleaned it out the first time when I got mine, and always check the jets. Some people have reported getting mismatching jets out of the box.

    I will keep you all informed.

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