1975 bs38 choke question

[thatguy]

Hay guys I've searched for 2 days for the answer and have not found it...

My question is were the chokes are conjoined togeather from the 2 separate bs38 carbs, there are 2 bras nipples that stick out were a rubber tube joins them. One of the bras nipples popped out and can slide in and out of the hole were it is suposed to go freely. How do I secure it? Or is there some were I can buy a new one from any where?

Also how do you sink these carbs if there are no nipples on the manifolds? ( I have already bench synced them and rebuilt them, looking to know how to sync while bike is at idle)

Just some clarification needed on the next question.

What would you recommend for a rough jetting as a starting point, if using yamama pipes and the black foam filters from pandimonium.
( I heard up a size on the pilot and 2 on the main, is this accurate or am I wrong)

 

[bosco659]

Not sure which brass nipples you're referring to. Most of the brass pieces are press fit into the bodies. Hopefully there’s still a bit of friction left. Clean the nipple and carb body well with alcohol and reinstall the nipple with a light coating of a fuel resistant sealant like 3Bond, or maybe even JB Weld. Experts can chime in here.
On the choke body there is are slotted screws that can be removed and temporarily replaced with M6x1.00 hose barbs for your sync guages.

 

[bosco659]

Slotted head screw just above throttle shaft spring assembly. Screw with red washer. One on each side

 

[thatguy]

Thanks dude!

 

[grizld1]

www.amckayltd.com/carbguide.pdf . OP, if your carbs have one choke valve and a crossover, don't bother looking for those slotted plugs; there were no ports for manometer barbs before the C model (1976), and the single choke valve indicates an earlier carb. Right, JB Weld. Use the original, not JB Quick.

 

[gggGary]

Brass tubes should be a tap in fit if both tube and bore are clean, smooth.

 

[thatguy]

Interesting I'll look to night and post pics.

 

[hovel]

Also how do you sink these carbs if there are no nipples on the manifolds? ( I have already bench synced them and rebuilt them, looking to know how to sync while bike is at idle)

I have a '74 TX. I can sync the idle by ear with the mufflers off. I listen to the "crack" in the pipes. This won't work with a 2-into-1 system which is one of the reasons I don't like them. Your cylinder to cylinder timing has got to be spot on. Once I've got the idle about where I want it, I sync the cables. I barely crack the throttles open with the twist grip, hold it there and measure the space between the throttle arm and the idle stop screw with a feeler gauge. Then I ride and listen. Regarding all the speed and mixture adjustments you can make, no two carburetors are exactly the same.

 

[thatguy]

These are my carbs. Grizld1 was right no port for sinking. Looks like I'll have to get some manifolds with tubes on them

 

[grizld1]

The only good carb boots are ARS, available under the Tour Max label online and from any shop with a K&L Supply catalogue. For some reason the ARS boots for BS38 carbs are no longer available with vacuum barbs; only the BS34 boots have them. It may be possible to drill and tap the carb bodies for thread in barbs. I like hovel's drill; guys have synched those carbies without manometers for years. But hang on awhile and I'll pull a salvage carb out of the stash and see what can be done. I'll post pics if I can come up with a solution. If not I'll let you know.

 

[thatguy]

Thanks dude that would be sweet. Thanks for the info

 

[toglhot]

I have a 74 which had no way of syncing, so I drilled a hole in the manifolds and pushed a barb in.
The brass tubes can be expanded with a drift of the right size, slip the largest drill bit that will fit through the tune, then grab the next size up, using the blank end of a drill bit, grind it down to size if it's too big, taper the end, place it in the brass tube and tap with a hammer, no need to go the length of the tube, about 5-6mm will do the trick. It will only require expanding by about .5mm - .10mm, so the brass is unlikely to split.
Jetting varies from bike to bike. I had straight through pipes and pods on my 74, didn't require re jetting at all., but I've since changed to VMs.

 

[thatguy]

https://www.mikesxs.net/yamaha-xs65...bs38-oem-447-13555-01-00-447-13565-01-00.html

I was thinking of trying these out. Would these work? They say they are for the 1972 -1977.

 

[grizld1]

The only boots I can recommend are ARS. Boots from Mike's XS used to have all the rigidity of stiff foam and failed quickly. I don't know if the new management at Mike's XS has done anything to improve them, but as far as I can tell they follow the founder's tradition of making no changes to anything that sells. Caveat emptor.

 

[toglhot]

JBM!

 

[Bumblebee]

I bought a set of carb manifolds with manometer barbs from Mike's XS within the last 6 months or so.
They seem to be fine. Maybe a little softer than stock but I've had no trouble.
My only complaint is the barb interferes with removal of one nut of the intake valve cover. If I remove the rubber cap then it's not a problem. Just seems like a little alignment hiccup that could have been avoided.

Overall, I'm happy with them.

I added a pic to show the interference. It's no problem to remove the dome nut.

 

[hovel]

I have a 74 which had no way of syncing, so I drilled a hole in the manifolds and pushed a barb in

There is no way in hell that Toglhot's barb installation cost $54, and you get to put them anywhere you want. If I were doing this I'd modify a spare set of manifolds so I could go back to stock in case I screw one up. Oh, who hasn't done that before.

 

[grizld1]

Here's the solution I guessed at but didn't want to recommend before I'd done it successfully. On the underside of the carb spigot, you'll see a brass plug. Punch the center of the plug, level the carb in a drill press, drill and tap for M6x1.0 thread. You can use M6x1.0 threaded barbs, 6x1.0 manometer hose adapters, or drill out the ends of a couple of M6x1.0 grease zerks to release the ball and spring, as shown in the photo below (thanks for that tip Mr. Gary, Master of Machines and Machining!) Cover your home made vacuum port with a screw and fiber washer when not in use.

 

[grizld1]

The pic doesn't show it clearly, but the new vacuum port opens behind the throttle plate, which is where it needs to be.

 

[TC2000]

My xs1 has a pipe connecting both intake manifolds; I suppose it has to be blanked off in order to make any meaningful vacuum comparison