'79 XS650 Special Low-Effort Resto

Yes, you need 6mm barbs for the vacuum ports on the BS38s. Some make them out of grease nipples (drill the ball and spring out).

Grazie, Twins.

Okay! So, I got the XSCharge ignition from Mike's yesterday. Got it all installed after some fiddling, and the bike fired right up with the new ignition in its starting setting (middle of the slot). Now I just need to get it properly timed, which leads me to a question. The instructions, such as they are, provided my Mike's are a joke. They say to time the bike at idle. Other sources (mostly here on the site) say to time the bike at 3000 RPM. Which is correct? I'm inclined to believe info here on the site, but I'd like to double check first.

Actually, you check it at both. You want to make sure it's not advancing too much. That may require setting the idle timing a little retarded. It all depends on how much wear your advance unit has. When new, it gave exactly 25° of advance. As they wear and loosen up, the amount of advance can begin to grow. If set on the middle mark of the idle timing "range", it may go past the full advance mark. You compensate for this by setting the idle timing a few degrees retarded, still in the "range", just over towards the right side of it .....

Ah, right on. It seems that my advancer is a bit tired, 'cause it idles in the correct range just fine, but the XSCharge unit has to be retarded past where its "slots" are. That, and it advances way past the advancement mark when revved to 3000. I reckon I need one of those advancer unit rebuild kits from Mike's.

Yes, maybe some new weights from Mike's will fix you up. The wear on these units usually occurs to the little tabs. The sharp corners on the slots in the little center disc that the tabs stick into cut into them over time. So the unit ends up retarding more, not advancing more. But the overall effect is the same - a greater amount of total advance .....

B E H O L D


It's (mostly) done. I ended up having to rebuild the mechanical advance with new weights, springs, and clips, and use the center section provided with the XSCharge ignition to get it to run correctly, but now it's all tuned up and ready to go. It still needs a touch of fettling (re-tighten some nuts, adjust the clutch that isn't disengaging totally, address a tiny fuel leak, fix/replace the speedometer drive, etc.)

That video was shot about two minutes after starting. Cranked right up with no choke after sitting since last night. The video below is after a quick rip up and down the street. This thing is so raw. Very elemental. I'm pretty happy with the way it came out.

So, an update!

This thing is still definitely haunted.

When I can get it to run right, it runs like a champ. The problem is that it's hard to keep running when the mixture screws keep backing out of the carb bodies and falling off. I haven't lost one yet, but the last time I took it out it started running like shit and when I finally got it home I discovered that the mixture screw on carb #1 had backed all the way out again and was balanced precariously there on the carb body. These are K&L aftermarket mixture screws, so I changed out the o-rings with ones that are a little more robust to A: seal them better and B: make sure they don't back out anymore. Fingers crossed.

I also failed to bleed the rear brake properly when I first reassembled it, so I have to do it again. I hate this rear brake system. The one on my XS850 (which is damn near the same) is easier to bleed. My Mitivac hand pump was broken, so I was trying to bleed it the old fashioned way (with the caliper removed, dangled over the swingarm, and clamped to an old rotor I keep around for this kind of thing) and it absolutely refuses to bleed. I have a new Mitivac on the way.

Also, something weird is going on with the speedo drive. I swear that I can see it moving inside when I turn it by hand, but it doesn't turn the speedo cable. I cleaned it up and greased it, but it seems like it's not engaging the drive washer. At this point I may just pick up a new one, they're cheap enough on eBay.

So, yeah. That's where this build stands - the constant fiddling zone.

Your mix screws should have springs on them to keep them at the setting you choose. I can see them backing out to the point of falling out if you don't have the springs.

I thought they should, but they didn't come with springs, nor did these carbs have springs when I got 'em. Also, the parts diagram doesn't show them. My Hondas all have springs on their mixture screws, and so does my 850. I honestly just figured it didn't have them, 'cause I've seen some other real questionable design decisions on this thing.

Part #40 .....

https://www.partzilla.com/catalog/yamaha/motorcycle/1978/xs650e/carburetor-xs650e

Unfortunately, you can't buy it anymore, lol.

Well, goddammit. Huh, I'll find some somewhere, I guess.

Fleecebay

https://www.ebay.com.au/sch/i.html?...H_TitleDesc=0&_odkw=2F0-14134-00-00&_osacat=0

Yeah, I saw those and just laughed and laughed and laughed. Then I went out and dug through my parts bins and came up with one spring that works and ordered a whole new carb rebuild kit just for the other spring. At least it comes with all the other parts I can use on other carbs instead of paying 15-30 bucks for a simple spring. I can't believe I blanked on the springs. I feel like such a moron, but alas, here we are.

Okay, something extremely weird is going on here.

These carbs are not the carbs this bike came from Japan with. I bought them off eBay last year because the ones that came with the bike were, frankly, so far gone I didn't want to deal with them. They were sold as '78-'79 carbs. I found a single spring in the box of carb bits and it fit just fine. I ordered a couple of cheapie rebuild kits off Amazon just for the springs ('cause it was cheaper than buying springs off eBay) that were labeled for '78-'79. Once they finally got here I learned that the springs they came with were too big and didn't slide all the way into the carb. I assume the rebuild kits are wrong, but it's both infuriating and confusing. How different were the pre-'78 carbs? I wonder if these replacements aren't '79-'79s. I now have a carb kit coming from Mike's that's '78-'79, see we'll see what happens.

Another thing, what do we think about rebuilding speedo drives? Mine seems to spin inside when I spin it by hand, but it doesn't spin the speedo. Are they worth taking apart, or should I just grab one off eBay?

Dont know of carburetors .. and have not thought this over.
But a spring is defined more ore less by the physical sizes .Thread ,diameter and spring diameter .
Pitch ( not sure if that is the right English word )
You have one spring as it sounds. If the function is to prevent the screw to come loose.
The local hardware or auto-supplier can have something close enough.
It is also possible to make your own springs but it can be to overcomplicate this

What about the old set of carbs you replaced? Can't you scrounge a spring from them?

I actually just found a second one hiding in my toolbox, of all places. So, at least that's sorted. What do you all think about the speedo drive issue, though?

Well, there's a washer with bent up tabs that fits into the wheel hub. The tabs fit into slots in the speedo drive and spin it as the wheel turns. If you force the speedo drive into the wheel without the tabs being lined up with the slots, you can bend them down. Then the wheel won't engage the speedo drive and spin it .....

Yeah, I have all that and the tabs aren't bent. I think the drive is just bad. I'll poke around for a new (to me) one. By the way, what do we think about running diesel oil (like Rotella) in our old engines? I see guys do it all the time with old cars they rescue because the diesel oil apparently has more stuff (minerals, zinc, etc) in it. Right now the bike has bog standard 10w-30 in it.