Carb ID help and 2 in 1 throttle cable question!!!

[Big_Al]

Hey, I have an 81 650xs that definitely does not have 81 carbs. Each carb has a throttle cable that goes to throttle assembly. Are these Solexs?

I'm trying to get rid of the old beat up dual throttle assembly. Does anyone know if the TC Brother Choppers XS650 2 into 1 Throttle Cable for Mikuni VM Carbs (http://www.tcbroschoppers.com/xs650-2-into-1-throttle-cable-for-mikuni-vm-carbs.html) can fit with these old carbs???

Are there any benefit to these older carbs or did one of the POs just swap better carbs and sell the bike with crappy ones?

 

[grizld1]

Your carbs are either 72-73 or 74-75; single choke valve on left carb feeding right carb through hose is the tell. If 72-73, the venturi floor will be ramped and carb top will be marked "Solex" and "Mikuni Kogyo" unless somebody swapped on later tops. Later carbs dropped the Solex stamp. 74-75 carbs will have rounded floor in the venturi. Read the Carb Guide for specs; there's a link to it in the Tech section.

Hard to know why the PO made the switch; originals may have been damaged beyond repair, throttle shaft bushings may have been shot, etc. Year-to-year changes were made for a number of reasons having to do with serviceability and regulatory compliance, and had nothing to do with changing engine demands.

Switching to a 2-1 cable may work for you, but the ends on VM cables won't work; they're much too small for your throttle shaft fittings. Soldering on new ends isn't a big deal; for instructions, search and you shall find, but be sure to measure and determine the length you'll need. Both Motion Pro and Flanders can make up a set for you if you can give them the length you need (note: cable lengths are specified from the ends of the cable end pieces).

 

[Big_Al]

Thanks grizld1! Spot on. The carbs have "Mikuni Kogyo" on top, but not "Solex." Soldering doesn't seem like much of a challenge, but it might just be easier to work with Motion Pro. I'll give them a ring this week.

Another thing, which is bothering me more... I bought the bike last summer, but couldn't work on it because I went away to school. In the meantime, I had some so-called mechanic tune up the engine and jet the carbs for me while I was away at schooll last spring. He said they were 79 carbs! I don't know where he pulled that out of, but I sent pilot jet and needles from 650 central for a 79 to him. After installing a boyer ignition, the bike was idling really well, but test drive not possible because of leaking petcock. Any predictions on how the bike will handle on test drive after I finish cafe build this month? I'm thinking it will ride like a lawn mower with the wrong needle in it...

 

[5twins]

The #120 butterfly plates indicate the carbs are '74 or newer. Older carbs used a #125 plate. If your "mechanic" installed '79 5O2 needles, the carbs will run very lean. The 5O2s are 4mm longer than the original 4N8 needles that came in the '74-'75 carb sets. The '79 carbs also used a different type pilot jet, a VM22/210, as opposed to the BS30/96 style that was stock in the '74-'75 carbs. That will most likely cause issues as well.

 

[Big_Al]

Oh, this labor of love...(sigh). Well, thanks for the heads up. Now I have to add re-jetting carbs to the this never ending laundry list. I was worried about finishing the build in time before returning to school, but now I also have make sure the bike can make it to school!

 

[Big_Al]

As in most cases, if you want something done right, you have to do it your damn self

 

[gggGary]

As in most cases, if you want something done right, you have to do it your damn self

Ain't that the truth! Unfortunately for me even that's no guarantee.
I probably have some spare needles to fit those carbs. They do look like they are in nice condition. The separate cables makes em a bit fussier but I am quite happy with how my 73 runs.

 

[Big_Al]

haha, yeah same here. I usually don't get it right the first or second time myself, but third time is the charm, well not for sanding and polishing my hubs at least. After three days of wet sanding, I still couldn't get past those damn oxidation stains. I gave up and outsourced those damn things to a guy with industrial buffing wheels. Hope they come out well.

gggGary, well I hope my carbs treat me as well as yours do.

Do any of you know what needle size I would need for free flowing exhaust and cone air filters for these carbs?

 

[5twins]

There really are no needle alternatives for these carbs so you just stick with what was stock, in your case the 4N8. You change mains and pilots, and play with the needle setting. Just be aware that the 4N8 came stock set in the 4th needle slot, not the (middle) 3rd slot like most other carbs. Usually, you need to lean the needles a step when you increase the mains more than a size or two. That would put those needles in the 3rd (middle) slot. For your intended mods, I'm thinking one up on the pilots and two to three up on the mains should do, and the needles leaned a step also.

 

[Big_Al]

Thanks for the summation 5twins. I do have that carb tech packet saved and have read thru it months ago, but I'm so busy in the garage nowadays and am rushing to get this bike done before mid August. If I pull this off, I hope to share my build. Cheers.

 

[grizld1]

Cone filters are a bad idea, especially on vacuum carbs. Uni foam filters are the best choice for what you have, if you must use pods. Be aware that pods will cause trouble if you let them get wet, and that anything except a still air box will cause issues, some more severe than others, due to turbulence across the port for the lower diaphragm chamber. The difference between low pressure above the diaphragm and atmospheric pressure below it is what lifts the slide, and turbulence will cause fluctuating air pressure below. Acceptable performance can be achieved with the right pods, but it's not an ideal setup (of course the undersized factory air box isn't ideal either).

 

[Big_Al]

Understood grizld1. Thanks. I liked the look of the Uni s anyway, but couldn't justify getting them since I already purchased cones months ago. Now, I have a reason. Geez, the tab keeps growing and credit card nears max . If anyone wants unused Cones, I will post on classified.

 

[Big_Al]

There really are no needle alternatives for these carbs so you just stick with what was stock, in your case the 4N8. You change mains and pilots, and play with the needle setting. Just be aware that the 4N8 came stock set in the 4th needle slot, not the (middle) 3rd slot like most other carbs. Usually, you need to lean the needles a step when you increase the mains more than a size or two. That would put those needles in the 3rd (middle) slot. For your intended mods, I'm thinking one up on the pilots and two to three up on the mains should do, and the needles leaned a step also.

So, I was working with 650 central to get the right main and pilot, and I had to double check what the needle jet was. Turns out the carb does not have original needle jet, but a Y31 aftermarket needle. 650 central 's rebuild kits for 72-74 carbs use Y22 needles. But on a search on google, a keyster carb rebuild kit for 1974-1976 contains Y31 and states that it is equivalent to 4N8-4 (http://www.power-barn.com/keyster-c...for-1974-1976-yamaha-xs1-tx650-xs650-ky-0489/). Any input on the discrepancy?

 

[5twins]

The needle jet and the needle are two separate components. The needle fits into the needle jet. You're talking about needles here. The Y31 and the Y22 are aftermarket "generic" needles. They may or may not work depending on the carb set they're used in. The Y22 is only suitable for the '70-'73 carb sets. Griz mentioned the raised floor in the main bore that these early carbs had. That required a shorter needle. The Y22 is the same length as the original 4JN19 used in these early carbs. The floor in the main bore was dropped starting with the '74 carbs and that requires a longer needle. The Y31 is that generic one however it is 1mm shorter than the original 4N8. That means clip positions will be off one. The 4N8 in its stock #4 slot will equal the Y31 in its #3 slot.

 

[Big_Al]

Then #2 slot for the y31 needle it is... to match my mods. Great stuff. I would be lost without your help. Thanks guys.

 

[5twins]

Yes, there are other carb kits for some of the later carbs that incorrectly supply the Y22 needle. It's like 4 or 5mm shorter than what came stock in the newer carbs ('74-on) so there's no way it would work. The "-4" at the end of the needle number really isn't part of the needle number. It just indicates the clip position it's run in.