Mikuni BSW30SS Carb Info

[MelodicMetalGod]

It seems that these carbs are not terribly common, even here in "GS Land". Even searching Google, I get 6 hits or less when searching for these carbs. Therefore, I'm reaching out to anyone and everyone here who may have some resources of any kind relating to these carbs. Here's what I can tell you about them:

1) They're on my bike (1985 GS550ES, a TSCC model)
2) They're a pair (2 barrels in each body, feeding 4 total cylinders)
3) The model # doesn't seem to be indicated on the carbs themselves. I've gotten the BSW30SS info out of the Clymer manual.
4) Googling "Mikuni BSW30SS" gets 3 hits, only one of which is in English.
5) Googling "BSW30SS" gets 6 hits, only four of which are in English.
6) Searching for "BSW30SS" here on the forum gets only 21 threads, most of which are referencing BSW30SS only in passing.

It's amazing to me that there is so little info on these carbs, so if you know anything about these carbs or where info on them might be found, please post it up.

Thanks all!

[MelodicMetalGod]

The following information was submitted anonymously in the "carb oem spec as per factory manuels" thread. However, my carbs do not share the 43410 stamp. Instead both carb bodies are stamped with 43560 and another number, 493. Are these number relevant or are they just some sort of tracking stamp? Does the info below apply to all BSW30SS carbs or just ones that share the same stamped numbers?

83 GS550E
Mikuni
BSW30SS
30 mm

It should have 43410 stamped on the side

Fuel level: 6.5 +/- 0.5mm (.26 +/-.02in)
float height: 20.5 +/- 1.0mm (0.81 +/- .04in)
Main jet:
cylinders 1 and 4: 95
cylinders 2 and 3: 102.5
main air jet: 1.0
Jet Needle: 5C64
Clip position: 1 groove from top
needle jet: P-2
Throttle Valve: 120
Pilot Jet: 35
Bypass: 0.8,0.7,0.8,0.8
Pilot outlet: 0.7
Float valve seat: 2.5
starter jet: 55
Pilot screw: Preset

[SqDancerLynn1]

The two bbl Muniki won't claim them neither will Suzuki They were only used for two years? Don't give up their are several people that have some experience with them

[distraction628]

try this thread

http://www.thegsresources.com/_forum/showthread.php?t=100520

[Nerobro]

They're much less weird than you'd be led to believe. They're just the same as 4 seperate carbs except they share a vacuum diaphram and a float bowl. Oh, and they share a choke circut as well.

They did come in several sizes, as small as a 26 IIRC and as large as a 32. They are the bastard children of mikuni though.

The smaller carbs came on the GSXR250, 400, and Bandit 400. The larger ones came on the KZ1300. I also vaguely recall some GS twin using a BSW carb.

My question for you, is what information are you looking for? IF you're worried about tuning, I think distraction posted the right thread for you. They really tune just like any other CV carb.

[MelodicMetalGod]

Thanks for the responses. I must say that I didn't see anything but similar questions in the thread posted by distraction628. Did I miss something over there?

[MelodicMetalGod]

They're much less weird than you'd be led to believe. They're just the same as 4 seperate carbs except they share a vacuum diaphram and a float bowl. Oh, and they share a choke circut as well.

My question for you, is what information are you looking for? IF you're worried about tuning, I think distraction posted the right thread for you. They really tune just like any other CV carb.

I don't think they're weird, but definitely less common. The sheer lack of reference material in this day and age is truly amazing to me.

I don't necessarily have a specific question (yet). Rather I was thinking that I'd try to build up some reference materials for when I do have questions, which will very likely occur when I get into the tuning after I've completed the cleaning.

Actually, if you look at my 6:11 pm post from yesterday, I would like to know if that info is valid for these carbs in spite of the stamp difference. I'm thinkin' probably so. What are your thoughts?

[550ERAT]

Is There Adjustment In The Chokes? My Carbs A Re All Cleaned Up And Tuned, But It Still Has Issues Idling Cold.

[skreemer]

the stamp on the side makes no difference the info garnered from the Hayne's is pretty much dead on.

There maybe some tweaks needed on the air/fuel mix adjust screws (pilot screws) but it should be OK.


ERAT:
In the middle of the carbs is a knurled knob... it's the idle adjust... screwing it to the right sends the RPMs up and the left in the opposite direction... Make quarter turn adjustments... after each 1/4 turn rap the throttle a couple of times and then wait for it to settle. MAKE SURE THE CHOKE IS OFF...

if this doesn't fix the issue go on to the next step...

If you haven't already drill out the air/fuel mix screws. Start at two turns out and then slowly go down till it idles right. (IIRC 1.25 - 1.5 turns out is the "correct" number) Though I notice mine gets flaky during this time of year depending on time of day because of the temperature swings.

WARNING: Be very careful about grounding these screws... I had one ground and I had to drill the bloody thing out... they are soft and crappy and you will stip the heads or get them stuck all the way down if you don't take it slow and careful... (I completely destroyed 6 screws and a half rack of carbs...)

[550ERAT]

Thanks for the info....I already drilled the plugs out and the screws are 3 turns out for it to run decent. I've tried all the other things, just not anything with the choke. I am wondering if because the carbs were so bad, that other things were adjusted to compensate. All the usuall things are fixed..intake o-rings, carbs rebuilt, new plugs. I am also replacing the voltage reg since my batt wasn't charging. Could that have anything to do with low idle issues?

[Nerobro]

If the charging system is shot, the bike will not idle well. Don't ask me how I know this................

[550ERAT]

If the charging system is shot, the bike will not idle well. Don't ask me how I know this................

HAHAHAHAHA I WON'T. I GUESS IT'S JUST ONE OF THOSE THINGS. SEEMS EVERYTHING HAS AN EFFECT ON SOMETHING. ONE THING FOR SURE, I AM LEARNING A HELL OF A LOT ABOUT THESE BIKES. HOPEFULLY WHEN I GET THE RUNNING ISSUES SQUARED AWAY, I CAN WORK ON GETTING SOME NEW PLASTICS.

[LeeGS550E]

Have you adjusted your valves?

550ERAT,
I'm going through the pains of getting my old basket case 550 back on the road. I was having problems getting her to idle at all (carbs rebuilt and cleaned many times over). On friday I went through my valves, and saw an immediate improvement. Just a suggestion.

[skreemer]

BTW my numbers were a bit off.... the fuel air mix screws with the stock setup should be out from 3 - 3.5 turns... adjust for your needs from there

[MacGyver]

BTW my numbers were a bit off.... the fuel air mix screws with the stock setup should be out from 3 - 3.5 turns... adjust for your needs from there

Up here in Calgary (1070m/3510') I had the best results at around 2.5 turns out. 1.5 was far too few turns out. If turns out are richer, then it would make sense that at lower altitudes 3 to 3.5 turns out would be best. My suggestion, split the difference and start at 3 turns out.