Carb Identification Help

[neobrien]

Hello All,
My name is Nick and this is my first motorcycle project. I pulled out my carbs to rebuild them when I ran into a problem. First of all these are carbs are off a 1978 XS400, the top is labeled “MIKUNI KOGYO CO.LTD JAPAN” (figure 1), the inside diameter measures 34mm and inside the float bowl is stamped “227” (figure 2). They look like other BS34’s (figure 3 and 4) so I originally assumed these where Mikuni BS34’s however, when I searched for a rebuild kit at mikesxs I noticed the float bowl gaskets that match my carb do not match the float bowl gaskets for a BS34 (figure 5 and 6). When I looked closer I noticed the BS38 rebuild kit gaskets looked much closer to mine than the BS34. This got me wondering what model carburetor is this and what rebuild kit is right for it, any help would be appreciated!

http://www.mikesxs.net/products-36.html#products

 

[bcware]

I have a 1978 with BS34 carbs; those are not them. I can't tell you what they are, only that they are not original.

 

[mpetry]

Not a clue

 

[Wolfe_11B]

Mikuni MK1 BS34's.

Apparently the MK1s came on the early XS360 as well. Probably how your 400 ended up with them.

 

[neobrien]

so they're not BS34's for sure but we think they're MK1 BS34's does anybody know where I can find info on MK1's?

 

[xschris]

They look like they are off a mid 70's kz400. They are close to the xs360 but not the same. The bowls are different. The xs360 uses a 145 butterfly valve. I also notice a few other things also. As for rebuild kits the float bowl gasket used in the bs38 should work as well as the o-ring for the needle jet.

 

[neobrien]

So if I buy the BS38 rebuild kit I should be fine since the gaskets are pretty close and the seals are the same.

 

[xschris]

The bowl gasket, float needle and seat (#2 size) carb choke gasket should be the same. The needle jet o-ring http://www.mikesxs.net/product/48-5020.html should work. But without knowing the exact carbs you have some of the sizes on jets and the types they are may be different. The xs360 uses a different type pilot jet than the bs38 and the xs400's bs34. If you take yours out and post a pic and the numbers on it I will try to help.

 

[neobrien]

Thank you xschris! I can post a picture of the main and pilot jets and list their numbers tomorrow. I've compared the carbs I have and a BS38 and from the picture posted it seems they're very similar,

 

[xschris]

My xs360 carbs have the same mouth as yours. But yours has different fuel line setup and what looks to be a vacuum line next to the choke. Like I said gaskets and o-rings should work it's the jets I worry about. What do your diaphragms look like?

 

[neobrien]

Sorry it took me so long to post, my pilot jet is 7.5 (Figure 1) and the main jet is either 5 or 7.5 (Figure 2) it was difficult to tell. The diaphragms don’t appear like they need replacing (Figure 3, 4 and 5). I plan on putting pod filters and may or may not be straight piping the bike so, I planned on re-jetting the carbs anyway.

 

[xschris]

Pilot jet should be a 17.5 and the main 135. Those type of pilot jets are hard to find. They where only used in a few carbs (76-77 xs360 and xs750 that I know of) and I have only seen them in two sizes 17.5 and 20. The xs250 which was not sold in the u.s. used a bs32 carb also used them I do believe. The main jets are easy to find. The diaphragm looks like the xs360 but the needle attachment is different. It will be hard tuning a set of carbs that came off an unknown bike model.

 

[xschris]

This thread show the difference between the xs360 pilot jets and the ones used in the xs400. http://www.xs400.com/forum/showthread.php?t=13892&highlight=xs360+pilot+jets

 

[neobrien]

After emailing customer service at mikesxs.net we determined (based on float bowl gasket and diameter) that I have carbs off an XS360. I understand that the air bleed pilot jets are hard to come by and they’re not interchangeable with non-air bleed but; that’s a problem for future me right now I’m just trying to get the right parts to get the bike running. Will the different needle attachment for my diaphragm cause any problems with the rebuild kit I’m planning on buying?
http://www.mikesxs.net/product/48-1920.html
By the way I understand that some of these parts won’t work but it’s easier to just buy the kit than to buy each part individually.

 

[xschris]

I noticed that is don't come with the o-ring for the emulation tube. http://www.mikesxs.net/product/48-5020.html

 

[neobrien]

I'll add that to the growing list of parts this awful carburetor needs. Thanks for all your help xschris!

 

[xschris]

I think I have found your carbs I believe they are off a mid 70's Suzuki GS400. http://www.ebay.com/itm/1977-Suzuki...rbs-/361253442445?hash=item541c62138d&vxp=mtr If you look up other years around this time period they do very some but look a lot like yours. This should help with finding parts and settings. Tuning them for the xs400 might be a bit of work.

 

[neobrien]

Thank you xschris now the question is do I try and tune those carbs to my bike or just buy ones for the xs400? I'll have to think about it

 

[Curseduth]

Thank you xschris now the question is do I try and tune those carbs to my bike or just buy ones for the xs400? I'll have to think about it

Did you ever get the bike running on these?

 

[neobrien]

No because school started it is my intention to work on them over fall break, thanksgiving break and winter break.