mikuni BS38 identification

[lil2lo]

Hi,
I'm new on this forum. I looked already many times, because it's a good source of information. But now I have a question that I can't find in the archives, so here it is.
I'm building a xs650 chop and I'm almost finished, but there are some last hurdles to take. I'm having issues with the carbs. I rebuild them (they were in need of a rebuild and they were ugly black). But now I'm trying to find out which type bs38 I have, so I can order parts and tune them. I looked in the manual and on the net but I can't place them.
here are some specs:
- bike is a 2F0
- butterfly valve 120
- needle jet Z-4
- float needle 2.0
- main jet 144 (i'm sure this isn't original)
- pilot 27,5
- the needle is the one with the plastic disc

I already ordered a carb rebuild kit #48-7879 from Heiden tuning (same as mikes xs, but over here in Holland). The new float needle valves are smaller in diameter (I thought they were all the same). Actually nothing in the kit is the same. This is not Heiden to blame, I'm sure the carbs are not original and therfore I ordered the wrong kit.

here are some pics

Left is float valve from carb, right is the new smaller one from the rebuild kit for 2f0 bikes.

That's not really water

 

[DogBunny]

Those are not XS650 carbs. They look similar to the 76-77 XS650 carb set, but that's not what they are. No XS650 carb ever used a Z-4 needle jet. The float valves are a type not used in XS650s. Differences in body, chokes, and float bowls. I think Suzuki used Mikuni BS38s, maybe Kawasaki too, whatever you have was never on a Yamaha. Someone who knows there stuff might get them to work, but I suggest you look for another carb set. If you want to stay with BS38s, go for either the 76-77 XS650 set or the 78-79 XS650 set. They are superior to 75 and earlier XS650 BS38 carb sets.

 

[lil2lo]

Thanks man. I knew something was not right. The engine ran when I bought the bike. So I think it's worth a try.
Tx750 used z4 jets. But I'm not sure these are from a tx750.

 

[5twins]

TX750 carbs were not linked. They wouldn't have the casting on the bottom for that angle bracket. What you might have there are Kawasaki KZ750 twin carbs. They've been modded to "work" on the 650.

http://www.partzilla.com/parts/sear...79/KZ750-B4/CARBURETORS (KZ750-B4)/parts.html

Originally, they used a 2 cable push-pull throttle cable assembly that hooked to a cam between the carbs. Someone converted that to the single cable lever on the outside of the left carb's butterfly shaft, like a 650 carb set uses. The float bowls may have been swapped for 650 ones as well. The original Kawasaki ones take BS30/96 type pilot jets. Your bowls are the '78-'79 650 VM22/210 pilot type.

If you could figure out proper jetting, you can probably get these to work. It may involve needle and needle jet swapping too. But, it would be interesting to try and get that Z-4 needle jet to work. I don't see why you couldn't with main and pilot sizes tailored to work with it.

 

[lil2lo]

I think you might be right. I compared the carbs with kz750 carbs on internet and they look the same. They were also bs38's so it seems. The float valve looks the same as the ones in my carbs.
I'm gonna have a try with these. At least now I know what parts to order.
Well thats just another piece of the puzzle solved. The ignition is a story on it's own.

 

[ChrisH]

I have the same problem with my 76 xs650, question I have is it possible to change the internals for a carb repair kit

 

[650Skull]

hey ChrisH, welcome. This thread's last post is over 5 years old.

Start a new thread with your problems. What bike/Model you have, and a bit about your capabilities and bike experience.

And lots of pics............even if they are only of boxes of parts

 

[grizld1]

Memory of this one is more than a little foggy on this one, but I seem to recall that there was some jet in those carbies that was unique to them and had no equivalent in any other Mikuni jet--PJ or NJ. Might have been workarounds possible by tweaking secondary effects but I beat feet instead of getting involved: not my monkey, not my circus.

Chris, welcome, please read what's been written on carb kits. If you buy your brass individually and avoid the kits you may pay more, but you'll avoid a world of grief..