Re: silicone for assembly, I just bought this from Ace Hardware. Plumbers grease, 90% silicone, safe for all rubber and plastic. And super slippery stuff! A little goes a long way. I used it today. :)
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Cool! been using a dielectric grease but like that plumber's stuff! Need to get through the troves of info here yet.
Note to self don't buy used southwest carbs, heat and dirt.
yes genuine yammie (mikuni?)TS seals, had poor luck with the mcmaster seals long ago. They just aren't the correct shape to work well here.
Later carbs have longer bushings not sure on exact year/changes. Throttle shafts are brass and they tend to get burrs in the butterfly area, you should be very careful on removal, I find myself doing fine (1000, 2000 grit) paperwork here and there, so they come out of the body without scraping the bushings on the way through. Carry on!
 
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First of all, thank you so much 2M for hanging in here with me and for all your guidance and advice.

I see what you are referring to now with regard to the longitudinal shaft play, how it occurs with butterflies open and it not being an issue. Makes sense. With everything properly aligned and tightened in the closed position, no lateral movement in the idle circuit, which is what we are after. If it occurred at mid or upper ranges wouldn't have a significant effect I guess.

I measured the more meaningful vertical axial movements of the throttle shafts and results are posted in the revised carb measurement chart - post #73, page 4. .002' and .003". Don't know if this is enough slop to be problematic, but guess we'll see soon enough.

Forgot to check throttle bore measurements. :doh: Done now and results posted in said chart above. I think we're OK here as they range from one low 37.93 mm to 38.00 mm and most being close to 38. These probably fall within spec?

Also had a look at the throttle shaft bushings on the 78/79 carb bodies. I don't know how to tell if they are brass or bronze but they have very fine serrations/splines?.
The outside bushing surface is serrated (too small to photograph) which raises a couple of questions. (letters this time....lol)
  • a) I wonder how these were manufactured? I'm thinking probably placed on a locating shaft and pressed into a smaller bore in the softer Zamac carb body material. Can't see that the carbs were cast around these. But who knows?
  • b) These bushings do not extend the full depth of the throttle shaft bore (once again hard to get a pic) but rather sit against a lip the thickness of the throttle bore wall. Maybe after these bushings are pressed into place they, and the carb throttle bore wall lip are machined to 8 mm. Whatever the case may be with that I wonder if there is a repair solution for worn out shaft bushings on these older carb sets. Could one not just ream out a larger bore, even a stopped bottom bore to leave a lip, and then machine and install an 8 mm ID sleeve? If this could be done would maybe save the fate of some sets. I wonder.
  • Thinking again (dangerous again) Even if these are cast into place in the shaft bores they are now centered and one should still be able to ream and sleeve shouldn't they? I know Xsbob's concern was pulling the entire bushing and then not having the true centre but what if we just machine the existing centred bushing?
I have followed your advice while reassembling my carbs.
  • all seals and recesses well slathered with Permatex dielectric grease. Couldn't get any other silicone's today. For some reason everyone wanted a holiday up here today.
  • pressure on throttle shaft ends to assist return spring pull
  • Backlight to centre butterflies, well centered and nice fit top and bottom. I always checked this before but never with the additional push on the shaft.
  • gggGary,interesting you would mention the burrs. while none at the butterfly areas there was a slight wear line on one shaft where it met the throttle bore wall. Maybe some grit got in there and caused a little damage over time. My Autosol was closer than my fine W/D grits so it worked. lol.
So we're all studied, measured, and buttoned up again and ready to mount back on the bike.

Good Lord willing and the creek don't rise I will be able to get at that tomorrow and enjoy a nice long test ride.

If not, these will go into the material collection bin for that Gingery lathe I've been wantin' to get around to.
 
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Robin, I don't know, I think I'm catching your carburetor addiction. Haha, it's actually starting to become fun. Every time I pull them apart I start eye balling some component and thinking, " you know I could probably polish that and maybe it would work a little smoother. Haha"
Every time I work on them I get a little more comfortable with them.
Btw, when I was working on my carbs this morning, at first I tried using di electric grease for assembly, and while I know it's harmless, maybe even good for rubber, it felt a little gummy/sticky in operation. If you can find some of that plumbers silicone grease at a home center, it's pretty nice stuff. At the store, I was looking where they had lubricants such as WD-40, but this stuff was in the plumbing supply section.
I wish you success, it seems you and I have spent an inordinate amount of time trying to rectify carburetor problems.
I think we're due buddy!
 
Hey Bob, sorry. There will be a local chapter of carbaholics anonymous your way.

You're right as opposed to the viscosity of Vaseline it is a little gummier, but I went with what I had. I will check around for some though for other sets, thanks for the tip.

And you're right, we need a break. Odd how we have both been dealing with similar issues at the same time. Should have done one of Pete's video chats.....lol.

Best of luck tomorrow my honorary Canuk friend.
 
Thanks for that gggGary. That was a great movie! Have to watch that one again.
 
Man, it's great that you and Mailman are doing the carboholic simultaneously. Great for cross checking. Too bad the transporter's down. We could all meet up at GggGary's place,

And drive him nuts.

...I measured the more meaningful vertical axial movements of the throttle shafts and results are posted in the revised carb measurement chart - post #73, page 4. .002' and .003". Don't know if this is enough slop to be problematic, but guess we'll see soon enough.

I think that'll be OK. It's kind of a trig problem. Fully closed, the butterfly plates would be at about 12.5° from vertical. On my carbs, the idle stop screws are run down about 1/3 turn from fully closed, which opens the plates a couple degrees, which produces a slight gap between the top/bottom of the plates and throttle bore. Been awhile since I calculated this, recall that produces a gap of about 0.005"-0.006", which was dangerously close to my slop value. Your 0.002"-0.003" slop probably isn't enuff to allow the plates to contact the bore at your idle setting. Unless yours is set less than 1/3 turn from fully closed.

...Forgot to check throttle bore measurements. :doh: Done now and results posted in said chart above. I think we're OK here as they range from one low 37.93 mm to 38.00 mm and most being close to 38. These probably fall within spec?

That sounds to be more circular than mine. I'd just like to know what other carbs measure at. If you look at good, hi-dollar carbs, the throttle bores are perfectly circular. And, reputable carb performance shops insist on that roundness. It does affect idle and off-idle response. Don't know if just mine are uniquely oblong, or if it's common with our carbs. Kind of a personal project.

...Also had a look at the throttle shaft bushings on the 78/79 carb bodies. I don't know how to tell if they are brass or bronze but they have very fine serrations/splines?.
The outside bushing surface is serrated (too small to photograph) which raises a couple of questions. (letters this time....lol)
  • a) I wonder how these were manufactured? I'm thinking probably placed on a locating shaft and pressed into a smaller bore in the softer Zamac carb body material. Can't see that the carbs were cast around these. But who knows?
Zamak has a lower melting point than bronze.
They could've been cast-in.

...
  • b) These bushings do not extend the full depth of the throttle shaft bore (once again hard to get a pic) but rather sit against a lip the thickness of the throttle bore wall. Maybe after these bushings are pressed into place they, and the carb throttle bore wall lip are machined to 8 mm. Whatever the case may be with that I wonder if there is a repair solution for worn out shaft bushings on these older carb sets. Could one not just ream out a larger bore, even a stopped bottom bore to leave a lip, and then machine and install an 8 mm ID sleeve? If this could be done would maybe save the fate of some sets. I wonder.
  • Thinking again (dangerous again) Even if these are cast into place in the shaft bores they are now centered and one should still be able to ream and sleeve shouldn't they? I know Xsbob's concern was pulling the entire bushing and then not having the true centre but what if we just machine the existing centred bushing?
Yes, that was my original intention with my carbs. Modifying a 10mm (or 3/8") ream, with a long 8mm (or 5/16") shaft, and backwards cut the throttle bore to accept bushings. The details are in that other link posted earlier. The question is: Will 10mm (or 3/8") exceed the OD of the existing bushing?

...So we're all studied, measured, and buttoned up again and ready to mount back on the bike.

Great. I'll be listening for a loud noise, booming outta the northeast.

...If not, these will go into the material collection bin for that Gingery lathe I've been wantin' to get around to.

OHBOY, another project!
 
Aaaaakk! Just remembered something else.
Mailman, this is for you, too.

Have a look at these progressive throttle plate positions, and note the location of the metered (mix screw) idle port (left smaller hole), and of the first transition port (barely visible at the top of the butterfly plate). The large hole is the discharge port of the starter (choke, enrichner).

As the throttle plate is opened by fractional turns of the idle stop screw, the first transition port becomes more and more exposed.
(Clicking on a pic will take you to that album's pic)











Okay, so what's so all fired important about this? It shows the progressive exposure of the 1st transition port as the butterfly plate is opened. The metered (mix) port and the 3 transition ports are all fed by the same pilot jet.

These pics are of my '71 XS1B carbs. Yours may be different, so don't expect these pics to precisely apply to yours. The important thing is to note, while the carbs are still off, just when the 1st transition port becomes visible, as in how much turn of the idle stop screw. Best would be if you took pics like these, a progression of 1/4 turn increments. And use those pics later for reference.

Later, after the carbs are installed and you're doing the tuneup thing, make note of how far, from fully closed, you've turned the idle stop screw.

On an ideal carb setup, only the metered port is exposed, giving you greatest control over the idle quality with the mix screw. If the idle stop has to be opened more, to keep the engine running, the 1st transition port will start to become exposed, and deliver fuel. As this transition port becomes more exposed, the relative influence of the mix screw will be reduced. Eventually, opened enuff, the 1st transition port will be delivering so much fuel as to make the mix screw adjustments ineffective.

So, while you're doing your carb tuneup thing, make note of the idle stop screw position while fiddling with the mix screw. If the idle stop has the plate(s) too far open, the mix screw may not give you any adjustments. Conversely, if the mix screw isn't giving you any response, consider that the idle stop screw may be opening the butterfly too much.

Clear as mud???
 
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Great points 2M! I've long said if the idle screw is very far from "normal" it'll never run right, and you haven't found all the problems yet....
This is a rebuilt but not run BS34 set so I'm not positive that's a "running" screw setting yet I'll snap a shot or two of the running 78-79 set's idle screws
 

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Once again 2M thank you for your input and for all the time you have invested here. Wish you could get that transporter tuned up. You and gggGary and so many others here are up at the top of my 'would love to meet those guys someday' list.

Your 0.002"-0.003" slop probably isn't enuff to allow the plates to contact the bore at your idle setting. Unless yours is set less than 1/3 turn from fully closed.
OK, thanks for that confirmation. IIRC I was further out than that with this set.

It does affect idle and off-idle response. Don't know if just mine are uniquely oblong, or if it's common with our carbs. Kind of a personal project.
When my 74/75's make it back home (should have just bought some bottoming taps for those float bowl screw holes and been done with it), I will get and post the measurements for those as well.

The details are in that other link posted earlier. The question is: Will 10mm (or 3/8") exceed the OD of the existing bushing?
Yes, I remember reading through that a few times and that would explain where I got the idea. I will get a picture and rough measurements of the bushing OD / wall thickness from my other 78/79 carb on the bench. All I can do is eyeball it, but it will give an idea of how much there is to play with.
You are suggesting a 10mm ream, which would mean that the new sleeve would have a 1mm wall thickness minus a little maybe for clearance for insertion/adhesive. Don't know if that would be required but I'm curious if adhesive would be necessary to prevent wear on the outer sleeve wall from rotation as well.
But, ignoring this rambling, I'm envious and wish I had the equipment that I could machine a 10mm bushing with a 1mm wall thickness. You have some nice toys.

Clear as mud???
I am amazed to say, "absolutely perfectly clear". Not because your explanation is lacking, but that I have absorbed enough about these carbs that it makes total sense. I will photo-document and make notes of all of this. Interesting to have another visual check procedure and a way to preset idle screw better than my, 'ya that looks like the right amount of gap at the bottom' method.

Once again, thank you for everything.
 
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2 different 79's with 78-79 BS38s, one stone stock in every regard, the other with lots of minor changes. Note how close the two screws exposed length between bracket and throttle arm is. these are both idling at about 1K RPM stone reliable once a bit warmed up, walk away and come back in 10 minutes she's still ticking over exactly the same.
 

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Great thanks gggGary, Finished chores etc. so getting ready to hit the shop. I will see where mine ends up and post a comparison pic.

Wish me luck! LOL
 
PS if you get it running half way decent........ RIDE THAT Be-itch! Put some miles on, stop, grin and do it again. No matter how much I work on carbs and engines it seems like after 2-300 miles on the road they always are running better than when first started.
 
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After reading Mailman's latest posts it looks like my carb brother and I are both fighting uphill battles here. Maybe our 77D's are twin sisters and they're PO'd.

Well it started really easy, almost like 1 1/2 kicks. Still need to do the starter clip fix but with the way things are going THAT job is way down on the list. As she always starts so easy I don't mind kicking her for now. Just have to be careful who I say that too.
Right side idled perfect putt putt but left was hunting and missing a little.

I should mention that I have only carefully bench synced and set idle screws to factory 2 1/4 turns out. It ran, so I rode.

Observations:

If we're playing stump the chump, I'm certainly the chump and I'm stumped.

After meticulously cleaning this set (again), and assembling / setting up more carefully than ever before they are actually running no better and maybe a little worse than they were before I replaced the leaking throttle shaft seals.

I did however take gggGary's advice, thank you. Figured they are running 'halfway decent' so I rode for an hour. Thought maybe they just need to settle in and I needed a ride. That WAS fun and sure felt good even though I knew she wasn't right yet.

At mid and upper throttle ranges, smooth, steady pull, no hesitation, but that's the easy part isn't it. The hard part is getting it to run well slow.
The idle is still erratic at stops, surging higher, turn down idle screw. ride a bit, idle surges again and hangs for a bit before dropping and wanting to stall, then turn up idle screw. Butterflies are moving freely, no binding.

Am also getting a little backfire.

I have sprayed carb cleaner around exhaust manifolds before with no apparent effect but I checked exhaust manifold studs after it cooled and one was a little loose so I tightened. Although I don't think it was loose enough to cause a backfire leak. Haven't restarted to verify yet though.

It stalled on me one time (in an empty parking lot fortunately) and I could not get her to fire. Almost like there was no spark. I pulled the plugs and didn't see any spark? So we both took a break. After a few, saw spark and she fired again and I pushed my luck for another half hour and then headed home.

Once home the rougher idle / missing / slight backfire had switched sides. Also at idle speeds of 800 - 1000 alternator was making some noise
I had never noticed before.

I pulled the plugs and they are carbon coated. Either it's running rich or maybe I have an ignition system problem?

I am wondering if something other than just carbs is going on here. Or I am experiencing an unbelievable coincidence.
It ran well on my first set of 78/79's until they warmed up and the damaged throttle shaft bore end allowed the seal to leak causing erratic idle. (They're still at the machinist).

It ran well on this set of 78/79's until they warmed up, exposing throttle shaft seal leaks, causing erratic idle. I then tore them down and went through everything recently discussed here, and they are now no better, maybe a little worse. In fact the erratic idle issue showed up right away and didn't wait until after riding for awhile.
Perhaps the carbs are good now and are allowing the problem that lies elsewhere to surface more readily.
Throttle always snaps right back so don't think cable is binding.

I'm not quite sure what to do at this point. I keep thinking everyone always blames the carbs first, but not sure where else to look.

Going to check timing again.
Cam chain adjuster is good.
No excessive valve noise.
Voltmeter was showing alternator is working but will check in the shop tomorrow.
Will do dead cylinder on carbs to get mix screws right
Will play with carb sync a bit but I can't see that it would be out enough to cause this.

I got no problem pulling the carbs again and going back in, can probably do that blindfolded, but I don't see the point.

I will spend some time going over things tomorrow and if anyone has any suggestions as to what else to check. I'm all ears.

Edit: Not quite ready to fire up the forge for that Gingery lathe just yet.
 
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My official "clutching at straws" list with maybe a life jacket or two in here.
Have you put a timing light on it and watched, especially at idle and revving up and down a bit?
Any "unusual" arcing at points?
Have points ever been changed or is it on some other ignition?
Has there been a sync done while running?
spark plug caps tested for correct ohms?
just for kicks n grins? try a set of BP6ES ,1 grade hotter plug.
ground wires correctly placed on upper motor mounts?
Condensers checked?
Voltage at coils checked
Put an inline spark tester on and watch in dim light.
 
Thanks for the reply and suggestions gggGary,

Reset points with dwell meter back on May 22.
Checked timing with timing light and reset at idle and full advance on May 22 trying to solve this problem on the first 78/79's. Will check again.
Didn't notice significant arcing but wasn't specifically looking for it. Will print off your checklist and have a look tomorrow.
Stock points ignition, could still be original, don't remember. I have cleaned and gapped and they looked to be in good shape without any major pitting, but didn't look under magnification. Have some from XS650 Direct in the parts box so could do.
Have not done any sync after bench, will try but this is petty erratic. Sure worth a shot though.
Brand new 5K caps and wires, but maybe should still test?
Will get some BP6ES.
Will check that ground. I did clean all connections but maybe in doing that I disturbed something.
Have not checked condensers. Will check the manuals on how to
What coil test should I do?
Will finally get one of those and do that.....lol. Love an excuse to buy a new tool.


Thank you again for your help gggGary. I was wondering if in fact I may have an ignition system problem and you have given me an excellent checklist to work through. I appreciate it and will go through everything tomorrow.

Take care

Edit: Noticed today that my dash headlight indicator lamp would occasionally come on and then turn off again. Inside the headlight bucket I spliced into the headlight circuit for the light in my voltmeter. Wonder if this is affecting things and causing my problems here? Guess I could disconnect all of that and see what happens.
 
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I would change out the points. They wear out and don't have to look particularly bad to have done so. It's suggested you change them every 10 to 15K because the springs that snap them shut can get weak by then. There's also an age factor at play here if they are the originals. Basically, they're antiques now, lol. They may not be closing positively and tightly enough each time to allow a proper spark to be generated. I ran into this problem on a local kid's bike. I told him to change the points when he got the bike a few years ago but he couldn't be bothered. Eventually it just quit running and that was the problem, the points. I installed new ones and the bike fired up in less than one kick. Really, it was running before I completed the first kick through.
 
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