Identify/info on these carbs...

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Milk_Jesus

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I received these carbs in a big trade for a bunch of junk I had laying around. Wanting to use them on my xs build, but I don't know ANYTHING about these carbs, or carbs in general. Help me out, what do I need to know/what can you tell from these pictures?

592B-436D-89C8-F7911FD30DB7-15294-00000E8E8F76A56A.jpg

C490-4DB8-9603-804D570652C4-15294-00000E8E8981670A.jpg

2868-48CB-AA38-509850FFD675-15294-00000E8E8399473F.jpg

C6CA-43EF-996A-96C99B219A3F-15294-00000E8E762B8547.jpg

6401-445F-949E-FF9D842883E8-15294-00000E8E6747A6ED.jpg
 
Mikuni CV carbs BS 34mm's such as supplied OEM to Yamaha XS 650's 1980 and later.
Look to be pretty clean and likely usable. Might want to get familiar with them. There's
a great carb guide available on this sites tech section. On the other hand,there's a number
of folks here who would be glad to take them of your hands via "classifieds" here. BOL, Blue
 
bluebikerblan said:
Mikuni CV carbs BS 34mm's such as supplied OEM to Yamaha XS 650's 1980 and later.
Look to be pretty clean and likely usable. Might want to get familiar with them. There's
a great carb guide available on this sites tech section. On the other hand,there's a number
of folks here who would be glad to take them of your hands via "classifieds" here. BOL, Blue
Click to expand...

weekendrider said:
34's from 80-81 model years.
Click to expand...

friend told me these are pretty much the worst set i could have. any recommendations on a set i should try to get?
 
Oh no! The guy the other day in England that opened his float bowl and found some shit like someone was rolling pizza dough has the worst set you can have! Opinions vary, but the 34's and 38's both have thier "particulars".
 
:twocents: Read....no really read this carb guide.... http://www.amckayltd.com/carbguide.pdf then use it as reference as you familiarize yourself with the carb set to evaluate condition and anything needed to set them right if they're not. Make sure jets and passages are clean and clear, o-rings and diaphragms are in good condition etc. Having a set in your hands to reference as you read this guide of 5twins & grizld1 is a great learning aid. Blue

ps: look around for the missing "butterfly bridge" that should join the two carbs at the 2 inside bolts of the topside diaphragm covers.
JBM Industries for Carburetor Boots and Diaphragms if needed
 
Last edited:
Someone has been into them recently(the brass crossover).
I would take them all apart but it is up to you.
The way the idle jet system works it is easy to clog at the mix screw point but
is also easy to clean.
Make note of your jet sizes and float setting. Look at the throttle plates to see if they look synced(same spacing). Check the diaphgrams with a leak test then look at them.
Who knows your may already have a pair with JBM diaphgrams, Johns needles and custom jetting.
 
bluebikerblan said:
:twocents: Read....no really read this carb guide....http://www.amckayltd.com/carbguide.pdf then use it as reference as you familiarize yourself with the carb set to evaluate condition and anything needed to set them right if they're not. Make sure jets and passages are clean and clear, o-rings and diaphragms are in good condition etc. Having a set in your hands to reference as you read this guide of 5twins & grizld1 is a great learning aid. Blue
Click to expand...

weekendrider said:
Someone has been into them recently(the brass crossover).
I would take them all apart but it is up to you.
The way the idle jet system works it is easy to clog at the mix screw point but
is also easy to clean.
Make note of your jet sizes and float setting. Look at the throttle plates to see if they look synced(same spacing). Check the diaphgrams with a leak test then look at them.
Who knows your may already have a pair with JBM diaphgrams, Johns needles and custom jetting.
Click to expand...

thanks for the help guys. i'll be getting some reading done this weekend it looks like. just throwing it in there, my friend who told me these basically suck also said they are "really restrictive and hard to jet, especially with straight pipes or pod filters" and also that the mid 70's bs38 that are linked are what he would recommend in stead of these. your thoughts?
 
They LOOK like 1980 XS650 BS34 brass float carbs but I would check fit and jets to be sure, the BS34's were mounted on a few different motorcycles with different centers and jetting. Hate to put a bunch of work in them and find they won't fit your bike.

Any bike is hard to tune to short straight pipes and pods but I just had a guy stop here last night with those carbs on a hardtail with short straight pipes and pods and it's running/sounding good. AFAIK it's still got stock jetting with the needle jet washer mod. Some restriction/baffles in the pipes is your friend for many reasons
 
gggGary said:
They LOOK like 1980 XS650 BS34 brass float carbs but I would check fit and jets to be sure, the BS34's were mounted on a few different motorcycles with different centers and jetting. Hate to put a bunch of work in them and find they won't fit your bike.
Click to expand...

well my engine is a 1980, so im guna go ahead and buy some manifolds and see how they fit just to get that out of the way.
 
I think my thoughts are biased. I follow Grizld1 and 5twins advice in the carb guide.
If you want other ideas read xsjohn's posts on the 650rider site and here, but mainly the 650rider site.
Then keep in the back of your mind these are mechanical and subject to wear so no two pairs act/react exactly the same.

Measure the mold lines on top of the throttle body. 120mm is the magic number, iirc.

Now that I take a second look, Gary's right. The drain plug says 79-80 with brass floats.
 
I prefer the BS 38's myself and preferentially the externally vented 584 type of the 76' & 77' model years but; that's also a bias issue and not nearly as important as knowing the intricacies of what you have and how they're supposed to work as Weekendrider and 3G's suggest. Go for the rubber quality of JBM's for sure! Blue
 
Drop the bowls and leak test the floats in a cup of hot water, bubbles = fail. ALWAYS check the o-rings on the float valve bodies it is RARE to find o-rings that aren't hard and leaking. If you can't remove the o-rings without them breaking they were crap and part of why the last guy gave up.
 
those are very!! clean paperwaights made by Mikuni sell them and buy some amals ezr to tune!!!

:laugh: no, those are ok carbs if you like mikuni good score :thumbsup:
 
If the slot is buggered let us know and I will reveal my super-secret get a fuggled idle jet/screw out without ruining ANYTHING tool and technique.

:doh:Groans from the peanut gallery......

The poor boober builder about shit when I handed him back his working carbs, because he KNEW that carb was, well, screwed. No visible slot remained and the jet head was mushroomed out to the bore from fruitless ever more desperate screw driver digging, And yet it came out intact, using only,
drum roll,

a simple home made tool.
You just knew that was coming didn't you? :wtf: Bwwaa ha ha.
And of course some patience. Funny how reminding yourself the alternative is replacement carbs can help that "patience" thing.
 

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