BS38 Carb Jets for TX650A - XSB

littlebill31

littlebill31

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I have a pair of '74-'75 BS38 carbs. So they are TX650A or XSB, old style 38's with seperate choke gasket,

bs38.jpg

I pulled the jets out and the main is a #160, pilot is a #25. 160? and a 25?
The owner said they work fine and just wanted a rebuild. The jets look nice and shiny new as well. I thought a #160 was only for BS34's. And that is a BIG jet too.
Any ideas on this? My bike is apart, so I can't put them on to try them.
Any ideas on a base to start jets at for pods and cut pipes?
Thanks all.
 
Yes, 160 is waaay big for the main ...... and 25 is waaay small for the pilots if it's the proper BS30/96 kind of jet. Maybe the pilot had to be so small because the main was so big.

Something you have to understand about CV carbs is they work on demand and the slide only lifts as much as the motor can use. This means you can put giant mains in there and the bike will still seem to run half way decent. The slide isn't lifting all the way so that big main isn't open fully.

If the bowls have been swapped for later VM22/210 pilot bowls then 25 is an appropriate size. Here's how to identify the bowl type. The air feed leading to the pilot jet is different between the two .....

BS38BowlTypes.jpg
 
my 74 TX650A runs the stock jetting 127.5 main 42.5 pilot this is with stock air boxes and dunstall replica mufflers
 
I too am wondering what a good jet baseline would be for the BS38s for air pods and open pipes.

I just pulled a set of my '75 and will be tinkering w these before I drop any coin on the XS keihin kit.
 
I have some questions with regard to the designation of model yr for the carbs you cite Bill? They look a lot more like 76 C or 77 D BS 38's to me. Recall that the 74 A and 75 B models were still "unlinked carbs" with dual throttle controls and only one carb having the enrichener circuit? Other info. on jets etc. from this chart may help too. Though who knows what's been done re jetting?

ie...lets re-evaluate what you're starting with? 5twins and the grizld1 ??? gang? Blue
 

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Yes, Blue, you may be correct. Those could very well be '76-'77 carbs. I can't tell for sure from one blurry pic, lol. If they have one throttle cable and a linkage to the other carb, VM22/210 pilots and bowl types, overflow nipples on the bowl bottoms, and 4M1 needles, then I would say they are '76-'77 carbs.
 
blackbetty said:
I too am wondering what a good jet baseline would be for the BS38s for air pods and open pipes.

I just pulled a set of my '75 and will be tinkering w these before I drop any coin on the XS keihin kit.
Click to expand...

This question is asked so regularly and the answer won't change: The baseline is up on or two jet sizes, it's different for everyone, you're going to have to experiment.
 
This carb, as you can see, has only the two bottom holes,
BS38 1.jpg
and a seperate choke body with a gasket,
BS38 choke.jpg
According to mikesxs carb ID, this is a '70-'75, and with a choke gasket, '74-'75.
carb_page.jpg

Vm bowl.
BS3822.jpg

Did I mention it belongs to a mythical wizard.
 
The "two holes" and both carbs with "enrichener" were also characteristic of the 76' C & 77' D model yrs. The throat vents (two more bigger holes) started with the 78'/79' model yrs.
not the 76/77 as implied by Mikes carb guide....I believe.

For example, here's a set of 76/77 BS 38's....
 

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The bowls are definitely '76-'77. The brass overflow tube to the left of the jet area indicates that. '78-'79 bowls didn't have that tube and '75 or older were BS30/96 type. If they're single throttle cable then I'd say you're dealing with a '76-'77 set. If you find 4M1 needles in there, I think that will be the clincher.
 
'75 and older carb sets don't have that area on the bottom to mount the angle bracket to. They were never solidly connected to one another as a "bank" and it's not possible to do so because the mounting holes for the angle are missing.

Since we've pretty much established they are '76-'77 carbs, try one up on the pilots (27.5), 4 or 5 up on the mains (132.5 or 135), and drop the needles one step.
 
It just so happens that there is a good set of 1976 C model BS 38's posted on ebay
right now with some good photo's for you to compare the set you have to. I think you'll find them virtually identical and will put your mind at ease re the advice you've been given as to their ID.

http://cgi.ebay.com/ebaymotors/Yama...rcycles_Parts_Accessories&hash=item1e62e56960

I've sourced several sets of this particular model also known as type II of the three I, II, III BS 38's sourced on XS 650's through 1979. They happen to be my favorites btw as the last of the pre-emission types which vent externally preventing the possibility of hung up float needle valves leaking gas directly into the engine. BOL, Blue
 
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Not fair lillbill your bench is neater than mine. My good deed yesterday was rescuing a set of BS34s I got as cores with a bolloxed pilot jet stuck in one body. had to drill, easy out, drill, easy out, finally drilled as far out as I dared and went in with a 5mm x .80 or .90mm tap. (damn my memory is short) It snagged the remains of the jet which came out with the tap and I saved the carb body! Woo Hoo. I got to use my newly acquired LH drill set too. The tubs of "need overhaul" carbs are overflowing.
 
Where are you guys getting all these carbs? Do you have ads in your local Craigslists for carb repair or something?
 
CL AD: Gary's home for wayward XS650 parts. Loving home provided, adoption service with full credential check and in home inspections. minor "rehoming" fee required.
 

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