Lets see a pic or three, there was no factory "single exhaust model".
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BS34 Jetting Question
- Thread starter nikiforova
- Start date
I may possibly keep the diaphragms from getting holes worn through them. It can't hurt.
nikiforova
XS650 Addict
Hey y'all. Been busy with school and work so I havent had all the time I once did to work on the bike and message this board. I ran the bike for the past few days about 30 miles round trip. All seemed well, but I decided to take the advice of this forum and remove one of my shims. Now it seems to falter just a bit. I got out for about 30 minutes around town (lots of stop and go) and towards the end of it I noticed some hesitation around what I'd guess is 3k-5k. Not really sure whats up with that, tomorrow we'll find out what happens at when i sit at 60 for a while with this needle setup!
Maybe 137.5 main jets at some point. If the jet needle has up/down movement with 2 washers it's ok. If it's bound (not moving) only 1 washer is possible. Or, you can go with a 336-Y-0 needle jet and a 51X11 needle set (richer) and then start over on main and pilot sizes
nikiforova
XS650 Addict
I'm keeping this in mind. I ran the bike about 20 minutes, with probable 10 being at 60-65mph and it felt okay at the higher rpms. When warming up and when coming off idle, it feels unresponsive and like its wanting to die on me. I am going to go back to the shim that I was running before yesterday because it was all around
I had fine movement with 2 washers. Ill probably pick up 137.5s and some 140's as well. Gonna go back to the previous washer setup here in a minute once I go to lab.
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The BS34's come set up very lean from the factory and, in fact, are right on the verge of being too lean. That means any little change made to intake or exhaust can throw them off and require some jet tinkering. That's also why even a totally stock machine benefits from bumping the mains up one size (to a #135).
When I got my '83, at first glance it appeared to be all stock. However, after a closer inspection, I discovered the P.O. had drilled extra holes in the ends of the mufflers .....
This made the carbs even leaner than they were so I needed to do some tinkering. Along with a 135 main (which I planned on doing anyway) I richened the idle circuit up slightly by reducing the air jets two sizes (135 stock down to a 130). The idle circuit air jets are another "tool" at your disposal for tuning the idle circuit .....
They don't have as big an effect as changing the pilot jet size so can be used more for "fine tuning" the circuit. For example, if a #45 pilot is too lean but a #47.5 is too rich, you can install the #45 and reduce the air jet a size or two. This will give you a richness level in between the 45 and 47.5. So, on my nearly stock '83 (drilled ends on the mufflers), the stock pilot combined with two sizes down on the air jet was good, and with the 135 main, it ran nice.
Now eventually, I changed the entire exhaust and installed UNI pod filters, so more jet tinkering was required. Now I did go up one on the pilots (to a 45) along with another on the mains (to a 137.5). But, two sizes down on the air jets combined with the bigger 45 pilot proved to be a tad too rich so I went back up a size on them.
To advise you better, we really need to know what changes and mods you have done to the bike, even any little thing like the drilled muffler ends on mine. Like I said, any little change can effect the BS34's.
When I got my '83, at first glance it appeared to be all stock. However, after a closer inspection, I discovered the P.O. had drilled extra holes in the ends of the mufflers .....
This made the carbs even leaner than they were so I needed to do some tinkering. Along with a 135 main (which I planned on doing anyway) I richened the idle circuit up slightly by reducing the air jets two sizes (135 stock down to a 130). The idle circuit air jets are another "tool" at your disposal for tuning the idle circuit .....
They don't have as big an effect as changing the pilot jet size so can be used more for "fine tuning" the circuit. For example, if a #45 pilot is too lean but a #47.5 is too rich, you can install the #45 and reduce the air jet a size or two. This will give you a richness level in between the 45 and 47.5. So, on my nearly stock '83 (drilled ends on the mufflers), the stock pilot combined with two sizes down on the air jet was good, and with the 135 main, it ran nice.
Now eventually, I changed the entire exhaust and installed UNI pod filters, so more jet tinkering was required. Now I did go up one on the pilots (to a 45) along with another on the mains (to a 137.5). But, two sizes down on the air jets combined with the bigger 45 pilot proved to be a tad too rich so I went back up a size on them.
To advise you better, we really need to know what changes and mods you have done to the bike, even any little thing like the drilled muffler ends on mine. Like I said, any little change can effect the BS34's.
Yeah
I shoulda said that; A possible issue is stacked washers can/could make the needles bind, stop a slide from dropping, as long as the installed needle can be "wiggled a bit" it's fine."your washers might be thinner than mine.............."
nikiforova
XS650 Addict
I see. Ive been messing around putting washers in all the places for the past couple days and I definitely "fucked around and found out" for myself with the two washers under the clip. Im running it currently with no washers under the clip and that seems to be working. Just to make sure I am understanding this correctly, placing washers underneath the clip will richen the midrange, and placing one above would in theory lean the mix, but it actually does not do anything.Yeah
"your washers might be thinner than mine.............."
I took it out for about an hour yesterday setup like that and I got some breakups through the midrange and into the upper. It wasnt starving like it had been in the past, rather, it will run up smoothly, cut out for a second, come back in and continue on its merry way. I struggle to imagine that this is rich breakup since im only up one size on pilots and mains with my current mods. I'm also not so sure I would describe this as lean stumbling as said in the carb guide. I just dont have enough time or experience with this to determine which it is.
You are right; washers ABOVE the clip will do nothing. with this needle the only adjustment you can make is to raise it slightly with the washer.
Following is not official, just what I think is going on with the BS34 needle design.
This needle assembly is changed from the BS38 needles (which also evolved through the years)
A problem with needles is they tend to shake in the air stream in operation, causing a lot of wear to both needle and the jet orifice it slides in. The wear changes air fuel mixture in the critical midrange where the engine spends most of it's time. So high mile carbs tend to go rich in the midrange.
In the BS34 the spring and the shape of the pill are designed to reduce wear in operation, note the small raised tab opposite the pin on the bottom of the pill. (just left of the blue arrow in pic 1) The needle hole in the slide is large enough so the tab causes the needle to cock a bit, letting it lightly touch the brass jet on the engine side, reducing vibration/wear.
Stack enough washers to bind the spring coils and the needle mount becomes rigid, the needle JAMMED to the side, it rubs hard enough in the jet to stop the slide from falling. This is not good, LOL
@5twins @grizld1
Following is not official, just what I think is going on with the BS34 needle design.
This needle assembly is changed from the BS38 needles (which also evolved through the years)
A problem with needles is they tend to shake in the air stream in operation, causing a lot of wear to both needle and the jet orifice it slides in. The wear changes air fuel mixture in the critical midrange where the engine spends most of it's time. So high mile carbs tend to go rich in the midrange.
In the BS34 the spring and the shape of the pill are designed to reduce wear in operation, note the small raised tab opposite the pin on the bottom of the pill. (just left of the blue arrow in pic 1) The needle hole in the slide is large enough so the tab causes the needle to cock a bit, letting it lightly touch the brass jet on the engine side, reducing vibration/wear.
Stack enough washers to bind the spring coils and the needle mount becomes rigid, the needle JAMMED to the side, it rubs hard enough in the jet to stop the slide from falling. This is not good, LOL
@5twins @grizld1
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This washer mod (first used by the KZ1300 guys) is intended as a quick and dirty fix for the early EPA carb lean stumble in a completely stock bike. It's just a little nudge, if changes have been made to intake, exhaust, engine, true jetting work is going to be needed. Why tuners have selections of the various jets in many sizes.
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nikiforova
XS650 Addict
Yeah I’m jetted up one size in both pilots and mains. Right now needle at stock height. Uni pods and 2 in 1 exhaust. I don’t have a flat spot off idle, but in the midrange I get a bit of hesitation. I just can’t tell if it’s lean or rich. Im guessing lean? Anyone have thoughts?
I'm guessing lean at mid-range too. IME, anything over a 45 pilot will be too rich with that set-up. What are the current fuel screw settings? I think the answer is in the main and the needle height
The needle setting tends to show up as the slide starts to rise ie about 25-3500RPM
It's a bit hard to describe but a lean condition tends to act like a light switch, with quick on off stumbles. ut, ut ,ut. A rich condition tends to feel more blubbery. More throttle tends to make lean worse, rich better.
A lean stumble is literally a cylinder not combusting/firing for one revolution. ie; a misfire. Rich is so much fuel (a smoky fire) the cylinder mix burns slowly not giving the piston of good hard push.
It's a bit hard to describe but a lean condition tends to act like a light switch, with quick on off stumbles. ut, ut ,ut. A rich condition tends to feel more blubbery. More throttle tends to make lean worse, rich better.
A lean stumble is literally a cylinder not combusting/firing for one revolution. ie; a misfire. Rich is so much fuel (a smoky fire) the cylinder mix burns slowly not giving the piston of good hard push.
nikiforova
XS650 Addict
G
This was perfect and exactly what I was looking for. It’s definitely too lean in the midrange. Once I get to about 2500-4000 it wants to stutter quickly. My needle is stock, no washer. I’m going to pull my carbs and try to go one lol
nikiforova
XS650 Addict
Still too lean. Going to go up to 137.5 in my mains
nikiforova
XS650 Addict
So I did some digging and chatting with some locals at the shop. I’m running the Mac 2-1 megaphone exhaust. It’s got a baffle, it’s just still loud as hell.
137.5s came in today. Excited to try and get them in, ideally, later tonight or tomorrow during the day.
nikiforova
XS650 Addict
Update: The 137.5s seem to bleed over enough for my mid range to not stutter (at least on shorter rides). I didnt give it a wide open pull, or even accelerate that hard today. I might get on that and try doing it tomorrow. I also realized that the 132.5s the PO had in were not 132.5s and they were, in fact, 142.5s. I suspect they had been onto something good there considering how awfully lean the 135s were lol. Woulda saved me a big ole headache, but I guess im just bound to take unnecessary steps back and figure out where to go from there 
Yes, to really test the jetting on these CV carbs, you have to push them hard. Test using big handfuls of throttle, even wide open throttle. That will uncover any "glitches" that wouldn't show when riding easy.
