BS38 Carb Jets for TX650A - XSB

[littlebill31]

Some people hoard whole bikes. I just want carbs.....lots of carbs!!!!!

I talk to a lot of people and many shops that are using XS engines have gone to VM's. So, they sell them to me, usually for cheap or we trade. Many places tell me they suck, then complament me on my bike. ???

 

[YL82]

This thread looked like a good one to catch a ride on...

I pulled my BS38 (CV) Carbs off and disassembled them this past weekend.

Here's what I found (as installed by PO's) as far as installed Jets, etc.

Main Jets: 135 (small round type)
Pilot Jets: 27.5
Pilot Jet Style (based on Float Bowl type): VM22/210 Series
Main Nozzle (Needle Jet): Z-8
Jet Needle: 4M1
Needle Position: 3rd groove (middle)

Comment on Needle Jet Condition: No sign of O-rings on either Needle Jet. What symptoms would this cause?

What can be concluded from above Jetting?

When I bought the '76/C, I noticed that the air filters appeared to be a foam type and the foam had all but disintegrated, so there was essentially no filtration.

To remedy this, I installed a pair of K&N YA-1152's which fit nicely into the factory airboxes. I also installed new foam rubber strips in airbox covers to provide a little better seal.

Would the use of the YA-1152's necessitate re-jetting? I've got everthing apart, so now is the time. Not sure what to make of the jetting I found.

I'm going to replace all the jets and probably the floats since they are pretty crapped up and specifically the main jets are all mangled from screwdriver abuse (some by the current owner)...

Oh, I've attached some images that were taken on the right carb. Taken toward the bottom of carb just above bowl. I noticed that a throttle part (?) moved toward a post that has a threaded hole, but I've got no bolts/screws in the hole.

Am I missing a part?

 

[gggGary]

Q: Am I missing a part?
A: No the linked carbs have only one idle stop screw on the left side of the left carb.

 

[YL82]

Thanks kindly, gggGary.

You got the easy question out of the way!!

 

[5twins]

Your carbs are stock and original for '76. They have been re-jetted (mains and pilots). Needle and needle jet are stock. The needle jet requires an o-ring. It seals the jet into it's mounting hole. Without it, fuel could pass around the outside of the jet instead of just through it like it should. The size is 1mm thick x 4mm I.D.

The mains and pilots may have been changed for mods or they may have come from a rebuild kit. The rebuild kit offered for the '76-'77 carb set contains those main and pilot jet sizes and they are incorrect for the carb set. They are, in fact, the sizes for the '78-'79 carb set.

Here's a chart I drew up with the stock jetting specs. If the K&N filters are your only mod, you may want to jet back down closer to the stock specs. I would try a size or 2 larger on the mains. That will probably improve the top end performance with the new filters .....

 

[YL82]

To follow-up, I just got some information back from the PO who is thankfully very helpful.

Regarding previous mods, I learned the following:

The PO's Dad (original PO) installed some "performance pipes" on the C around 1980 and that may have been when mains and pilots were changed.

The PO also indicated that he replaced those pipes (probably in last 10 years) with what he calls OEM equivalent pipes, but he did NOT rejet at that time.

Correct me if I'm wrong, but I'm thinking that this mixture of facts and speculation, though somewhat enlightening, is not enough to change the recommendations you made in your last paragraph.

Thanks, 5twins!

 

[gggGary]

What 5 twins says, his word is GOLD!

 

[YL82]

Without a doubt!! I've learned that to be the case PDQ.

Simply wanted to share some information that was new to me re. my carbs...

 

[5twins]

I have a set of '76-'77 carbs that I've run and sorted on my '78. I have pods, a freer flowing exhaust, and minor porting. The biggest main I could run was a 132.5. That's why I feel the 135 is probably too big for yours. I would start your bike on a 127.5 and go up/down from there depending what road testing indicated.

 

[YL82]

Will do, 5twins.

Looking at Main Jet sizes, looks like I was 5 sizes larger than the original 122.5....

In addition to going down several sizes on the Mains, should I stick with the 27.5's on the Pilots or go back to 25's?

Thanks!

 

[5twins]

You can try the 27.5 pilots but with larger mains and pilots, you may need to lean the needles a step. If you're not happy with the idle and midrange response like that, put the needles back in the middle and install the #25 pilots. Larger pilots usually aren't needed unless you do lean the needle setting. That also leans the upper idle circuit and can create a flat spot just off idle in the idle to midrange transition. A larger pilot cures that.

 

[YL82]

Thank You!

 

[YL82]

Question about Float Bowls (BS 38 Carbs)

Is it presumably a good idea to install the float bowls with their matching carbs?

I soaked both bowls in the same container and I'm not sure which is left and which is right.



One of the bowls has a 1 inscribed on the inside and the other has 2 inscribed. Do these numbers correspond to left and right?

 

[5twins]

As far as I know, the bowls are the same (no difference between left and right). I don't know what the # indicates, different manufacturing run maybe? Maybe one has been replaced with a newer or older version?

 

[YL82]

OK, I won't worry about it, then. Thanks!

 

[YL82]

I was looking to replace the white plastic "shims" or spacers that go on the throttle shafts.

Clymer calls these "caps" and shows them on their Carb parts diagram.

Does anyone know where to buy new replacement "caps"? I've not been able to find these online.

The ones I have are probably fine and may just have to clean them and slap them back on.

 

[5twins]

Yes, just clean them up and re-use them. You're worrying about something that will have absolutely no effect on the carb function. Maybe if they were broken in half or something but otherwise - not worth worrying about. And it's a good thing too because you'd never find those parts, lol. Just make sure you put them back where you found them. Stuff like that really isn't illustrated very well in the parts diagrams. You need to take notes before you yank things apart.

 

[YL82]

So you're saying I won't be able to find new caps in French Blue to match my fuel tank and side covers? Crap!! LOL.

You're right, of course. They are fine, just need to be cleaned up.

I have taken a few videos (probably not enough!!) with my smart phone of how things looked and how parts came off (such as the throttle shafts, springs, seals and all those parts), so you're point is an excellent one.

 

[YL82]

Question About Carb Clamps (Replacement Thereof):

I plan to replace my 4 carb clamps. Where exactly do I need to measure to determine what sizes I need from Mikesxs? They have several sizes. I have factory BS38's and factory airboxes.

 

[5twins]

I don't care for the carb clamps from MikesXS. They use smaller diameter screws. I would renovate your originals. Switch the Phillips screws out for M5 x 16 Allens. Then you'll be able to clamp them fully until the 2 clamp halves touch.