Man, it's been 10 years but I snagged another XS.


XS650 Member
Reaction score
So it wouldn't let me login on my old username, Oxblood, and even though I have the same email it made me register again. Oh well.

Well I had a bit of an impulse buy and snagged "drag style" XS650 off of Speedandnoise. I'm a sucker for single down tube gooseneck frames. It was super rad but I realized I'm too old and fat to ride it as is.


So digging through my stash I figured I would move the controls and bars to build a simple chopper for my wife. Waiting on a few parts to button up the handle bars.


Going to keep things simple, she rides a Triumph with mids so I guess I gotta make myself some. All the guys I knew that made them seemed to have stopped. I also am looking to make a cleaner triple tree but that will come down the road. Oh yeah I'm stuck on my porch for now because I moved and haven't built a new shop yet ..

I'm a special education teacher by day and earlier this year I found a 3d printer in storage at the school. I hadn't played with them before but we had a blast making student projects. I liked it so much I picked one up for home and man it makes prototyping parts so much easier. Starting in on the mid control mounts. From cardboard CAD to 3d printed iterations as I refined the design.

I made a new throttle cable today and realized the clutch and brake levers I have are triumph style so I had to order a different set of cable nipples. Next project is figuring out exactly what carbs I have so I can get the right kits for a rebuild.

Carb kits aren't really recommended. Many come with the wrong size jets, but with your open pipes and pods, you wouldn't want that anyway. About the only thing that might be of any use is the float bowl gasket. You're better off just buying any individual parts you may need. That might be stuff like the float bowl gaskets and maybe floats or float needle and seat assemblies. Float needle and seat assemblies are best sourced right from Yamaha. A bit expensive but you know they'll work. The ones in the kits are aftermarket and their quality can be lacking. Many times they leak right out of the box. If you need floats, no need to pay big bucks for them. The BS38s use the common Mikuni VM24/171 float, available from many places for around $15 or less .....


Yes, you will need to determine the year of your carb set because re-jetting is based on what was stock for the year of the carb set, not the year of the motor. If you show us some close up pics of your carbs, we can probably identify the year for you. It's recommended you use only genuine Mikuni jets.
One more thing - those pleated K&N style pods will most likely cause tuning issues. They don't work well on these CV type carbs. Best pod choice is the straight foam UNI pod. For the BS38s you'll want the UP4200 .....

Uni Pod.jpg
Last edited:
One more thing - those pleated K&N style pods will most likely cause tuning issues. They don't work well on these CV type carbs. Best pod choise is the straight foam UNI pod. For the BS38s you'll want the UP4200 .....

Sweet, ordered a set of pods. The bike runs, started second kick for few days then the right cylinder dropped out and I noticed gunk in the right fuel line and no inline filters. The other issue is the carbs seem to be leaking, I can't tell if it just accumulating at the float drain or leaking from there. So I figured I would just get all of the gaskets, orings, and such and go through them. I'm more familiar with flatside mikuni's so I appreciate the help. I'll pull the pods and get some closeups later today.
There's only one o-ring in the BS38 carbs and it's the one on the needle jet, but you won't find it in any of the rebuild kits. You can still buy it from Yamaha but they want big stupid money for it, lol .....

If you do want an original, you can get it from Suzuki for a fraction of the cost .....

Needle Jet O-ring.jpg

But I've had good luck just using the readily available generic 1mm x 4mm size. But, you may not even need to replace it. The needle jet is a snug, push-in fit into the carb body. As long as the fit is still tight and not loose, it's probably OK. Check the fit by placing a finger on top of the needle jet and see if it wiggles at all in the carb body.
Been busy with irrigating the garden for my wife so I haven't had much time one the XS. Traded a buddy some parts for paint so that'll be exciting. Started stripping the spray paint off the engine. Other than that waiting on parts.

I read on one of the forums that this bolt was 10mm x 1.25 thread pitch. I ordered 4 not so cheap bolts and that does not seem to be the case. Anyone know what size it is?


That bolt size is correct, I just checked one .....


If those holes have been empty for a while, they often get all crusted up. You probably need to run a tap into them and clean the threads out. The original bolt is rather special. It has a washer attached under the head and it's 20mm length is just right to allow a lock washer on the bolt and to go through the flange on a headpipe then be tightened down without hitting the frame tube behind the bracket .....

So I pulled apart my carbs for a quick clean since I suspected the chunks coming from the gas tank may be causing issues.


Currently it's jetted at 30 pilots and 142.5 mains. One float was a touch high so I reset that and now it doesn't leak.

I fired it up and ran it down the road and think I fouled a plug. Tried swapping coils, then wires, then plug side to side it all came down to 1 plug. I had a chopper campout I sponsor so I loaded the bike up for the mountains. The campout was at 8600 ft, 1000 feet higher than where I live. The auto parts store didn't have anything in stock so I grabbed some ac delcos that came up in the cross reference.
I get to the campout and slap the delcos in. Dang, the little nub doesn't unscrew, broke one thinking it was just stuck. Frustrated, I throw in one ngk and one Delco, just setting the plug wire on the Delco because it won't clip on. Kick it over and I am fining on both cylinders. Yay! Now, to just get a plug.
The vintage goldwing guy says he usually has some but can't find any in his van. A while later a xs650 guy shows up, fresh from riding down to baja Mexico on his 650 chop. I bum a ngk off of him and happily run over to swap it in. Kick it over and now the other cylinder isn't firing. Well crap. Throw the Delco in and it fired. Pull the Delco out and start swapping everything around again. Comes back to the plug. The one that was in the bike not the one the guy gave me. So I'm just messing around and pull the wire, has spark. Start to put it back on and get close, it starts firing! Yay, I can ride now! Click it on and it stops firing. Hmmm. Pull it off and hold it close, it fired. Click it on, stop firing. Start google searching with one bar in the middle of nowhere, fun stuff. Came across a tractor forum talking about the plug may be fouled and adding an air gap increases the resistance forcing more voltage to overcome the resistance. Ok, that makes sense.

Still had some fun and ordered the ap63s that come up on the forum alot. I also ordered some ironhead fork springs because these are way too soft. Let's see what happens next.


Oh yeah my uni style filters got lost in the mail so I need to order a new set.
Last edited:
If you haven't done so, with the larger jets the needles in your carbs are going to need to be leaned a step, from the stock #3 slot to slot #2 (from the top).
Pulled the needle, finding a small enough snap ring plier was fun. Looks like it is on third slot with a shim. Removing the shim and putting it on 2.

That's not a shim, it's a washer that protects the e-clip from being fouled by the little spring and possibly dislodged. It should be there.

5O2 Needle Washers.jpg
Last edited:
That's not a shim, it's a washer that protects the e-clip from being fouled by the little spring and possibly dislodged. It should be there.

View attachment 245561

Ok then! Will be putting that guy back on. Tried an old dirt bike trick to clean the fouled plug and took it around the block. This bike is a lot of fun but a wee bit small for me.
I put the the washer back in and now I have some stumbling at about 1/3 to 2/3 throttle. Low throttle and wot throttle both seem strong.
Your K&N style pleated filters may have something to do with the stumbling. Remove them and take a quick test run before changing anything in the carbs back.

So I threw some unipods on there I had laying around from my Triumph, after I cleaned and oiled them of course. Set the gap on the ap63s to .035, the ngks that were in there we at .028 and .025. Huge stumbling in the mid range, decent power at takeoff and high rpm at 3 on the needle. Moved needle back up to 2 and took another run. Less stumbling in the mid range, top end seems to scream by the butt dyno, I was surprised when it first hit. I feel like a couple of pulls through the range were smooth and a couple stumbled. Gonna go read the carb guide again.

Last edited: