What do I have and what should I use

[Jasonbobb]

These are from an 80's era bike. They seem smaller with one throttle control.

These are from a box of parts I bought locally. They need a ton of work but seem to be right for the three mid 70's era engines I picked also.

So my question is? What carb set do I run on my 1976 engine? I'm going to sell the set I don' use to fund the overhaul of the set I keep. Thank you. Jason

 

[CDNTX650]

I would use the BS-34 (black ones) Stay in sync better due to being joined. Single throttle cable...Your stock airboxes wont work. I use those on my 74 and used foam uni-pod filters. Leaner jetted due to being from the 80's. But not to big of a deal to get around.

 

[jetmechmarty]

Jason,

Are these supposed to be XS650 carburetors? If so, the top set would be BS34 off of an '82 or '83 Heritage Special. I would use those. The bottom pair looks like what came on the XS-1 or XS-2. The Heritage Specials were the only XS650s with black carburetors.

 

[Jasonbobb]

Thanks CDN,,I just needed some feed back casue this is all new to me and I'd hate to pass up on a good set of carbs if they just needed some work. Could I re-jet the BS-34 to get away from the leaner jetting? If so what would you sugest for a stock motor with the thought of putting a cam into it some day.

 

[Jasonbobb]

Yes they did come off of that "year/style" bike. I bought a complete basket case,,with the milk crate and all and,,LOL,,Thankyou Marty

 

[Sn34ky]

first looks like bs34 and second are probably bs38 from earlier xs... I'm pretty sure someone gonna say bs34 are better carbs... they certainly better then those dirty un-linked 38s!

 

[hmusket]

Top carbs look like '82 or '83 BS34s. Bottom carbs look like '72 BS38s which use dual throttle cables. Just looking at the outsides, If it was me, I would probably go with BS34s, they look the better of the two, may have less issues (you won't know until you open them to see what the insides are like). Using the BS34s would mean having to get different carb holders and use pods. Is your bike a '76, single throttle cable?

Also for more research here's a link to the carb guide, well written by 5twins and Grizld1. It should answer a lot of questions and help you in your quest. http://www.amckayltd.com/carbguide.pdf

 

[XSLeo]

Your BS38 carbs are 72-73 carbs. The earlier carbs had an enrichener on each carb linked with a metal strap. In 72 they changed to an enrichener on just the left carb and linked it to the other carb with a hose.
All the years from 70-73 used a raised floor design. If you look in the air filter side of the carbs you will see that the floor just under the slide angles up close to the slide.
In 74 they changed to a round floor design. Like your BS34's.
On my 75 I have used a set like your's as well as the linked set for 76-77. I now have a set of the BS34's from an 82 on it. The earlier carbs get slightly more power at top speed but the BS34's give better throttle responce across the rpm range.
I would use the BS34 carbs. On your 76 using the bs34 carbs with Uni-Filters will run fine. Your stock side covers won't fit without trimming the lead edge. The BS34 carbs are longer and the lead edge hits the carbs.
Not a great thing to trim the covers.
Leo

 

[Jasonbobb]

Thanksyou for the info man,, That helps me out a ton,,

 

[CDNTX650]

Jetting . my 74 is near stock...mikes brit mufflers with unipods. I went up a size on mains and could have maybe went up a size on pilots. But at around 3.25 turns out on the scews it idles good and doesnt seem to have a flat spot. Pulls clean like this . Oh i have a pamco too. plugs were apways a bit dark for my liking...but i dont do alot of long rides. So i put autolite 63s in. Ngks were tan..but dark tan.

 

[XSLeo]

With the mix screws at 3.25 out I might go one up on the pilots. The stock mix screw setting on a 74 set of carbs is 3/4 turn out. The 3 1/4 out is very near the limit of the pressure the spring exerts on the screw to hold it in place. It would suck if the screw loosened up and fell out.
Leo

 

[CDNTX650]

Also not running bs38 either. Bs34 on my 74. but yeah one of these days ill put bigger pilots in.

 

[XSLeo]

Ok, I assumed you had 74 carbs on your 74, should never assume. On the BS34's the 3 1/4 is fine.
Leo