BS-38 carb expert needed!

warrenlevihursh

warrenlevihursh

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Hello,

I am working on a chopper basket case for my brother. Everything should be ready to go now except the carb situation. I have two sets of BS-38s. A 584 (earlier style) and 2F0 (newer style). I plan on combining these two sets for reasons that would take too long to explain, but I had some questions.

What I plan on using:

584 style carb body

Z-2 needle jet

502 needle

The diaphragm, bowl and slide from the 2F0 carb.


Will this even work and do I use the baseline jet specs from the body (earlier carb) or for the newer carb model to match the rest of the internals and bowl? Thanks!
 
What style is the 584 set? A linked set or "bank", or 2 separate carbs? Do you know the year? You can do the parts swapping you are thinking of if the carbs are '74 or newer ones. '73 and older carbs had a raised floor in the main bore and use/need a shorter needle. Match the jetting to the needle/needle jet combo. In your case, since that stuff is from a '78-'79 carb set, use those spec mains and pilots.

Mix screw setting will probably need to be figured out on it's own. The '78-'79 mix screw is an E.P.A. stepped style and differs from all the earlier ones. The setting spec for it (2.25 turns out) probably won't apply to an earlier screw.
 
Thanks! They are linked 76-77 carb bodies. Diaphrams are rough and the have weird y22 needles or something, so i think ill swap stuff over. Just wanted to make sure it was possible.
 
The needle jets (z8 and z2) dont seem to be swappable. The z2s are 5.7mm or so and the z8s are like 5.4mm in diameter? Im I wrong? Seems to tight to press in....
 
You can keep the '76-'77 bowls if you like, then you'll have an overflow pipe. That was eliminated on the '78-'79 bowls, I guess because of the vacuum petcocks and Yamaha felt the carbs would never over-fill. Well, that was then, this is now, 30+ years later, lol. It's nice to have that overflow.

I thought the needle jets were all the same diameter. If they're not, it's a new one on me.
 
TwoManyXS1Bs said:
Sounds like you and peanut are in the same boat.

http://www.xs650.com/threads/bs38-swopping-needle-jets-and-jet-needles.51676/

http://www.xs650.com/threads/uk-members-can-you-help-me.51693/

http://www.xs650.com/threads/can-anyone-please-provide-bs38-slide-specs.51773/

http://www.xs650.com/threads/well-well-well.51933/
Click to expand...

Thanks for the links. I just bought the correct 4M1 needles to go with the older carbs. Hopefully the diaphrams work ok even though they seem a little stretched out.
 
I just did some parts checking, measuring, and fitting. I compared the late model Z-2's to earlier Z-6's and Z-8's. All measure the same, about 5.7 to 5.8mm in diameter. I was easily able to fit the Z-2's into '76-'77 carb bodies and the Z-6's or Z-8's into '78-'79 carb bodies. I don't know where those Z-8's you measured came from but they're not right if they're only 5.4mm in diameter. Your '76-'77 carb bodies aren't right either if they won't take a 5.7 to 5.8mm diameter needle jet. Maybe the holes are just gummed up or corroded?
 
20180515_203922.jpg
20180515_203945.jpg
 

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Ok so the needle jets are actually z6. Maybe long? I guess the carbs are older then I thought. Can you tell from the picture? And do these pilots lool like bs30/96. They are 47.5. Will the y-22 needles work in this? The diaphram rubbers say bs-38 with a 77 on the other side, so im confused! Sorry for all the questions.
 
I think those are replacement diaphragms from JBM. Yes, those are older carbs with the raised floor in the main bore. That's why the needle jets are longer. Originally, that carb set wasn't linked but it looks like someone made it so, probably by swapping in later butterfly shafts. The Y-22 needles may work in those carbs. One thing of note if you're going to try to use them - those nipples on the inner sides with the black caps on them, they shouldn't be capped. Those are the vents for the float bowls and should be open to atmosphere.
 
I forgot to mention, yes, that 47.5 pilot jet you have pictured is the BS30/96 type. It will need to be run in the older float bowl and won't work in a '78-'79 bowl. The float bowls for the 2 different types of pilot jets differ in the way air is delivered to the jet .....

qj73qga.jpg


The VM22/210 type bowl delivers air to the top of, or above the jet. The pilot jet flows straight fuel. The BS30/96 type bowl delivers air to the bottom of the jet. The jet flows fuel/air mix. That's why the BS30/96 pilots used are so much larger (sized in the 40's) than the VM22/210 jets (sized in the 20's).
 
Well I couldn't get it to run. It would fire but not really want to idle. I realized this morning on the way to work I think I have the slides in backwards. I think I put the tappered end toward the motor, which I believe is incorrect. Ill check it tonight to be sure.....
 

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