MIkes XS PWK carbs

[skervey35]

Hey guys this has been touched on here before but im looking into getting a set of the mikes XS PWK carbs, seems like a good deal and it gives you all the things you need in a simple kit.

Well I will start by telling why i am looking to buy new cards. Got my bike running after it has been sitting for 3+ years. But only fires on the right side unless i gas it hard while not in gear or driving it down the road then the left side kicks in and there is a huge burst of power (as you would think) So looking into the carbs i found out that they are not a matching set and that one i believe came off a xs650 because of the way it looks. They are almost identical, until you open them up. So i rebuilt the bad one and cleaned it but still wont fire on the left side. I swapped plugs still wont fire, swapped needle with a newer 1982? carb still wont fire. Swapped needle with a 78xs 650 crab, still wont fire. Re jetted both and it still ran on the right and not the left. Replaced main and pilot to recommended size for my bike and the size up and down from that. ( and i cleaned the crabs between all of the swapping parts, and adjusted air/fuel with all setting as listed above...)

I also checked compression for both left and right it it was 155 on both sides. The valves are adjusted and the timing is right...

One last thing im going to check tonight is swap the coil just to see if the high RPMs give that coil more power to work. Its a long shot but worth a try.

So yes im looking to buy a brand new set of carbs mainly because i cant find another set of carbs for my bike and i wont have to worry about 30+ yeas of junk in the carbs i may get. So from what i have read and wheat i know the carbs from mikes XS will work on my little 1977 XS400D. I know i will have to jet the new carbs and pull them off the bike a few times but by now im getting used to it haha.

(just got done rebuilding a set of holley carbs for my dads old race car from all that i have learned from messing with my XS carbs ( and a little looking up on other forums about the holley carbs) but we are going to try and fire it up Sunday its been sitting since 1996 keep you finger crossed!)

Well anyone with any thoughts on getting new carbs or something i may be doing wrong?

 

[jmd_forest]

The standard carbs really are not that bad to work with but they need to be CLEAN CLEAN CLEAN. After cleaning install an in line filter and you should be good to go. I'd invest in an ultrasonic cleaning before I bought new carbs.

 

[skervey35]

Yes iv installed a inline filter and have used a few big cans of clearer on them. I think im having trouble just because some one along the line has swapped the new xs650 carb onto the bike and that is what is tripping me up. There is so many things that they could have messed up when putting the 650 carb on. I was thinning about swapping one of the other carbs onto the one working carb on the bike but i was told not to by a very trusted friend that rebuilds bikes for a living. I would love to have a ultrasonic cleaner but that a good bit of $ for something that still may not get my bike running.

By the way do you have a ultrasonic cleaner and if so do you mind me asking how much you sent on it?

 

[jmd_forest]

I do not have an ultrasonic cleaner. I usually strip the carbs completely, and I mean completely apart and use brass wire, steel wool, and a couple cans of spray cleaner. I suspect you could find an ultrasonic cleaning service for a reasonable price if needed.

 

[HoughMade]

No ultrasonic, but I boiled my carbs on the stove. Here is a link to what it takes to really clean these things, but before you spend more time on the left carb, when the bike is idling, (left filter off) spray starting fluid or carb cleaner down the left carb. If it fires, you have spark and the idle circuit is still dirty. If that is the case, follow the steps I have outlined and it will fire. You may still need to adjust jetting, but it will fire.

http://www.xs400.com/forum/showpost.php?p=64401&postcount=17

Keep in mind that XS400s have used a couple different Mikuni BS34s over the years, so you may just have a different year XS400 carb. Here is a pic of my stock '79 carbs for reference. They should be very similar to '77 carbs:

 

[HoughMade]

Also, check out these videos.

http://www.xs400.com/forum/showthread.php?t=6375

 

[skervey35]

Ya ill have to watch that some time when i have time looks like what i need to see. But im really ready to buy the new carbs they will look realy well with the style im going for and give me a power boost. Im still leaning towards getting the new carbs and selling the xs650 and newer xs400 carbs after soda blasting them and cleaning them up, to help offset cost.

 

[xschris]

Any pics of what you have? The best way to get all the crap out of the passages is to put 150lbs of compressed air through them. Did you sync them with a gauge or manometer? Also I would not mix a 77-79 carb with a 80-82 carb they are different.

 

[DanMach]

Lets do this right!

These are the carbs in question:

http://www.mikesxs.net/product/48-9010.html

From the reviews I've read online(on mostly xs650.com) they perform as intended on the 650. So what is the difference between a 650 and a 400 for the carb?? Not as much as someone might think.

The bigger engine is capable of creating a stronger low pressure system that as such "sucks in" more air and fuel. This means that the jets need to be bigger in an xs650's carb.

So we know that the xs400 will require smaller jets. I'd suggest you compare the xs400 carb jet size against the 650 and mimic that disparity as a starting point. This means the pilot(idle) jets, the needle(1/4 - 3/4), and the main jet(3/4 to WOT).

That MIGHT get you close. You might also get nowhere. It might idle but die past 1/4 throttle. It might idle, run SUPER rough at 1/4-3/4, and then run amazing at WOT...

It might also hiss and piss everywhere out of anger.

This will take some time to get right. Most of that time will be ordering parts and waiting. If it were me? I'd contact Mike and explain what you're doing. Tell him you know its gonna be a PITA and you're gonna have issues, but ask him to supplement the jets he sends.

Instead of +1 -1 from his stock size, you'd ask for predetermined jet size you are guessing at, and then get one leaner and richer from there. (You'll have to pay for an extra set of jets), and do the same with needle.

Just understand this will suck. If you are going to swap between old and new as you try to tune it, it will be even worse. Either way, those carbs are coming off 3 or 4 times and you'll need to do a fair bit of work.

 

[skervey35]

Yes im planing on pulling them on and off i know by working with the carbs that i have on the bike now becouse they have been on and off the bike about 12 times. I also just checked the coils and that work the same after swaped, running on the right side and not the left. So i know that this is a carb issue.

Here is the carb that is giving me all my truble

And thanks DanMach i never gave that any thought. But I do find it funny that the xs650 carbs are the same as my xs400 carbs (other than jetting and neddle) so I am wanting to think that that should not be a problem since they are almost the same carb. But thats just me thinking...

 

[skervey35]

OK i just saw this, this pic is of the carbs from the first time they came off the bike so they look dirty they are cleaner now. But it you look at 1 below you can see that it loks to have a small gap should it have a little bit of a gap there?

Also if you look at 2 there is no gap. I messed with the tuning of the carbs and it seemed that when i tried to get a gap on the right carb in this pic it only moved the butterfly on the left carb and not the right. I believe this because if you look at the springs in 1 and 2 they are not equal. Do they need to look the same?

So what im thinking is that since the left carb in this pic does not have a opening it is not allowing air to pass into the motor until is give the bike a lot of gas and then it opens up the butterfly and allows air to flow.

Am i thinking right or am i going crazy??

 

[xschris]

Not the same carb. The slide is bigger on the 80-82 carb witch is the one with the recessed pilot mix screw and there pilot system uses different air jets. Also I see the 77-79 carb( the one with the exposed mix screw) is turned all the way down. I can be sure the screw is broken off inside the carb witch will cause it to get no gas in the pilot circuit on that side.

 

[skervey35]

Well the carb that is #1 in the pic above is the carb that is feeding the running side of the motor so i have not messed a whole lot with it other than rejecting and cleaning, Do you know if there has to be a gap at the bottom of the butterfly or not?

 

[xschris]

You have to sync them with a set of vacuum gauges or a manometer, but like I said if your mix screw is broken off in the carb it wont help anyway. Take it out and look. With two different carbs it will never run right

 

[skervey35]

ok im about to pull the carbs back off now (just adjusted the carbs again but don't want to spill gas on a hot motor) i messed with the sync till it looked like both of them were just opened a little bit. It seemed to help once i got it on the road and gave it some gas the 2nd cylinder started up and keep up even to idle but as soon as i applied the clutch to start going in 1st the left side died again. So not im going to pull them clean them and check the fuel air screw on the working carb, the #1 in the pic above. Is there any way to check sync with out fancy tools?

And does any one know if there needs to be a gap at the bottom of the butterfly??

 

[DanMach]

Ignore this, crazy day at work. Speaking out of ass.

 

[skervey35]

Ya well more progress im able to get it to idle on both sides now after messing with the sync but when both are firing the motor revs up high don't have a tack to don't know how high i would say 3-4k. So i then pull the idle screw till it is not even touching and the bike still idles at around 3-4K if i tighten the idle screw it starts to idle higher. Iv tried messing with the sync the air/fuel screws on both carbs to get it to idle down but it stays revved high for the most part. It will start to idle down when i tighten the sync screw but then often the left cylinder stops firing and the RPM drop to 1000k area where they need to be.

Is there another way to get the bike to slow down on idle? and the fuel/air screw should be 3 terns back from all the way down right?

Well im going to pull them again and see what there is to see!

Also going to check the air/fuel screw on carb #1 when i get them off

 

[skervey35]

By the way thanks guys for all of the help! Im going to try and be on the road for the modders VS rockers in Charlotte!

 

[DanMach]

Sounds like your choke is stuck on.

 

[skervey35]

No the choke is free and goes into all 3 positions (all the way in of off right?) well i checked the air/fuel screw on carb #1 and its fine and put both screws 3 turns back and the same story... I also got both butterfly's closed and as synced as you can get without having the right tools. Its slowly getting better but till idles pretty high when both are firing and when i bring the idle screw back down i loose the left side of the motor. So for now it will just have to idle high. But it looks like rain outside so my work for tonight it done.

If any one has another idea about why it is idles so high do tell...