Mike’s XS pwk carbs

[WelderDave]

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.

 

[Dan]

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

 

[WelderDave]

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...

 

[WelderDave]

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.

 

[WelderDave]

Ok, so here’s an update.
The only jets I was missing are the 115’s for these carbs, I have literally all of the ones you can possibly get through Mike’s. So the 35 seems a little small, threw in the 40 and then the 45, and 45 was to rich, 40 is only slightly rich, 35 seems a little to lean. So I am running the 40, and waiting on the 115 mains because 110 appears to be to lean and 120 is to rich, then I’ll playbwith the needle but it’s pretty damn close. I raised my idle because although it says I was at 1500 my guages are slightly off, albeit close. I ohmed my coils and they came in at 4.3 ish ohms and I’m starting to wonder if I’m getting a cold spark. These are like 30 year old coils. I’m gonna need to use a spark tester to verify, because if I am, it would explain some of my issues.
More to come as I bear through all this, but I’m getting close!

 

[WelderDave]

So here’s what I’ve come down to. I’m using a 35 pilot, 115 main, 1.25 turns out on mixture screw middle notch on needle. Only slightly lean off idle, may move the clip down one notch to raise the needle and see but all in all it pulls and runs pretty damn good.

So I’m going to conclude this and say although these carbs aren’t perfect, they work well for a substitute to stock. My originals were screwed when I got the bike so unfortunately I don’t have anything to compare them to, but they work good. It wasn’t necessarily the needle profile like I thought originally that was off but you have to dial in which jets work the best, and dial in your mixture screw and idle as well. So a little finicky, but simple. If you need new carbs and can’t get stock ones and the price is right, I say go for it.

 

[WelderDave]

Hey, I want to give an update here as something of a fluke happened that turned out to be awesome.

So I had it about as good as it would get, previously posted, and My filters were bigger than I wanted, I went and bought some foam pod filters from eBay for about $30. They’re a pretty good quality, and yes they have that lip on the inside of them. But before I was gonna cut the lip out with an exacto knife, I decided to try it out as is, and I’m very happy I did.

I put them on there and took it for a drive to warm it up and it was stumbling on the lower and higher mid section of the throttle, so I lowered the needle 1 clip notch up. Still wasn’t quite right at idle, so I richened the mixture screw a tad, rpms came back up, and now it runs great. Main jet is a tad rich with the 120 and will drop yet to the 115 to test, but I think that slight restriction gave me that happy middle I was looking for that I couldn’t tune out. Who would have thought a pod filter with a lip would solve my issues.
Maybe these carbs are slightly to large or something for this bike, but I highly recommend a foam pod filter if you get this kit if you want to be truly happy with them.

I’ll consider this solved, and I’m very happy with the outcome. Been trying to get these right for quite some time and it did the trick.

Good luck, and I hope this helps some people if they decide to use these carbs!

 

[Alex650]

So your liking the 120? These come come with a set of 100, 110, and 120's. What do your plugs look like or what are you basing the performance off of? Do you have a sniffer or are you plug chopping?

 

[WelderDave]

Well it all depends on where you’re located on what’s going to work for you but for me this setup works the best. I didn’t do a plug chop, but my plugs have been a darker brown color. I was getting for a long time all kinda of sputtering depending on my carb settings and it would just move around between the ranges. The. 110 was definitely to small as it would loose steam on wide open throttle, and the 130 caused it to sputter at wide open theottle. The 115 and the 120 were very close, almost like I needed an inbetween. Then there was the problem with the lower range where it kept wanting to die off throttle. My rpm guage was off, reading higher than it really was, so I did raise it to where it’s supposed to be around 1200. I needed the 35 pilot jet on mine. Every once in a great while it would still sputter on the top end but everything else was darn near perfect. Once I put the foam filter on that had that little lip on it it has been running flawless. May be a tad on the rich side but better rich than lean. Plug looks a darkened color brown.
It’s been great all the way through the powerband in all gears since my last change with the filter, so I’m calling it good. Starts easy enough with choke till it warms up a bit and when warm starts right up after turning it off.

 

[WelderDave]

So I started with stock jetting they came with and it ran like crap, plug was showing lean. Jumped to the 35 pilot and it ran better, then jumped to a 120 and it seemed pretty good. Ordered all the pilots and the main jets from mikesxs just to be certain and tried all combinations I could, obviously 1 change at a time. Went richer and richer, on both pilot and then main jets and then adjusted the pilots again. Each change I adjusted the mix screw and then the needle in each setting. All test rode. Finally came back to the 120 main and the 35 pilot and it ran the best off idle, top end, mid range and everything. Only a slight sputter barely noticeable. Then I wanted to change to a smaller filter so I got the foam ones on there and I was gonna cut the lip out with an exacto but decided to try it with it first and I’m glad I did. Put it on there, rode it, made a little adjustment to the mix screw, and then the needle 1 clip setting, and after that there was no sputtering or hesitation anywhere from off idle to wide open throttle, and ran great. Swapped the plug, took it on a 2 and a half hour ride around the lake here and checked the plug and she looked slightly rich but everything was running fantastic, so I kept it.

 

[Alex650]

Hmm. I have been reading all over that these things are crap and I have been trying to deal with mine. I would have just got some cv's or some other carbs if I didn't get these with the bike. I am running a completely dropped down needle and a 145 main with a 40 for the pilot. I road around for about 40 min and I still have white insulators on the plugs. If I change the needle It bogs at the top super bad so I'm not sure where to go either. the next step down are the 120's If i was overly rich then I should be seeing some soot or black build up by now though. I'm also at 500 ft elevation so thats a 2 step at most in jet sizing.

 

[Alex650]

BTW. How does it feel when you hit 70mph? is it wrapped out or does it have a good amount of power at high end?

 

[WelderDave]

I’m at 791 elevation where I’m at in Wisconsin. 145 was way way to rich. Some people can make them work and others can’t, idk what the difference is but I’ve had pretty decent luck with mine. I had to get new carbs when I bought my bike and they were the first to come up that we’re apparently made for the bike. I suspect the opening at the mouth is slightly to big which is probably why leaving the lip on my filter worked it out.
I can get up to 80 if I downshift and ring it out, but if I accelerate like normal and shift normally I can get up to about 65 no problem. I don’t do any highway driving withbit though, mostly just to bum around town or take back roads is what I wanted it for and what a lot of people I’ve been reading use it for. I started out with getting my low end mixture right first on idle, then I worked from the top down again. You may have the same problem I originally had where one circuit was lean and the other was rich. That would make it harder to determine by looking just at the plug, not to mention gas quality.

I also went from 135 down as it started solving my stumble issue and top speed. To rich and you won’t hit top speed because it will bog. As I lowered the main jet and fiddled with the needle I was able to get higher and higher top speed and the stumbling was less and less. 115 seemed to airy and the 120 let me hit a higher top speed than the 115 and the 125, so I figured it would be as good as I get. The slight stumble off idle was resolved a little by the mixture screw, but then I added that new filter with the lip on it and re adjusted the mixture screw and everything smoothed out.

 

[Alex650]

Thanks for the info. Yea I have had a hell of a time trying to troubleshoot these thinks. I had a bad jetblock gasket and that caused a rich symptom I have the idle down just fine and now am trying to get the main. if your at the furthest out on a clip on either side you should go to a different jet so it you at 1 (bottom) you should go up a jet size and position 2. Im at 6 so I need to go down a few. It sucks that 4 strokes will pretty much always run and 2 strokes are more obvious with the jetting.

 

[WelderDave]

I had the 30’s, 35, 40, and 45 pilots in mine, 35 was best suited. You should have idle change with the mix screw inwards and if you screw out to far also, with 40 I got no change if I kept screwing it outward, so I kept the 35 and it’s at about 1.25 turns out. Then the main jet sounds like is to rich on yours if the needle is all the way down and bogs in other spots.
I’ve also tried all different clip settings with the 125, 130, 135, and 140 main jets. I kept lowering main jets until the bogging and sputtering stopped and I was able to achieve the highest top speed without any problems. Then I dialed in the needle. Still had the stumble but added the filter I told you about and it smoothed it out. I really do think these carbs are slightly to big. A lot of people actually recommend smaller carbs but I already bought these so o wasn’t spending any more. But it got them to work well.

 

[WelderDave]

Yeah, these were a tricky bastard. I thought I had to get a different needle profile but turns out I just needed to make the opening smaller I guess, lol. I fought with these for an entire season before getting them right. They’re finicky but once you’ve got it, they’re good.

 

[WelderDave]

Keep in mind, the pilot circuit is always feeding fuel throughout the rev range. It does have an impact.
Also make sure your valves are adjusted properly, coils and all are good, and your points are clean and adjusted.

 

[Alex650]

Got the valves and all that. You cant sync these due to there is no port on them and the boots don't have any either. I got a 130 and then ran it. Bog after 1/2 throttle. Then lowered the needle to middle position and its now holding strong and im getting a bit of grey on the plugs (would be brown but its new ethanol gas). Much better response and now I have the ability to do 70 no prob. So My stats are

40 pilot
130 main
needle at position 3

Im also at 430 feet and its 95 degrees with 65% humidity.


Thanks for the help.

Im guessing that since its a smaller diameter that the piston has more suction on it vs the stock 34s which are wider. I hope people read all this because I would hate to have let other people go through the same crap I did.

 

[WelderDave]

Yeah no kidding. They can be a pain but as far as “syncing” just make sure they raise, lower, and bottom out at the same time on the slides. That’s all you really can do with these.
Yeah your air is denser than mine at the altitude and you have a hotter temp and humidity than I do. That all takes its toll.

 

[Alex650]

So I just wanted to give an update. I was tuning the other day and decided to go lean my main jet out and overall. I wound up at 105's main and needle on position 2. Runs nice and brown plugs. If anyone find's this thread I have the mikes xs400 performance carbs. Bought in 2018.