CaptCardboard's Quandaries and Questionable Repairs

CaptCardboard

CaptCardboard

XS650 Enthusiast
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Location
North-Leftern USA
1975 XS650B

It seems like all the cool kids have build threads to document the progress they're making on their bikes. I'm not really doing a big restoration or impressive chop job, but I love vintage bikes and enjoy learning and tinkering with my beautifully janky, stinky, voluptuous machine.

Thar she blows:
Messenger_creation_678c069f-573d-402a-a4ca-cd3394637b44.jpeg


What I've found that's not stock/modified by previous owners:
Aftermarket gauges
Shorty exhaust
1976/77 BS38 carbs
Harley headlamp
Rat rod tail lamp
Pain in the ass flat brat seat

Cool stuff I've done to it so far:
Heiden Tuning sump filter
Heiden Tuning oil filter/cooler
Boyer Bransden electronic ignition
16 tooth front sprocket
Rubber ducky

I'll be doing my best to post all my half drunk ideas and ghost hunting expeditions here.

Questions to follow! ....
 
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So here's my first installment...
I've been tracking down some performance issues. High/inconsistent idle when the bike is hot, some lugging when I give the bike a touch of throttle, and backfiring on the right side exhaust.

I bought a bottle of starting fluid today and it looks like I've got a vacuum leak at the throttle shaft seal on the right side carb.
My rubber manifold boots look old and have some checking on the surface, but didn't notice any difference in idle when I hit them with starting fluid.

Obviously I need new shaft seals. I see some on MikesXS, but I've heard they're a less than stellar supplier. Are their seals adequate, or where should I find better quality parts?
Any little tidbits for removing and replacing these parts?
Thank you, you beautiful little babies.
 
XSTime said:
You can possibly prove your seals are leaking by dripping motor oil on the shaft seal area in the crack...
Click to expand...

I figured squirting ether on the seals and hearing the idle increase was proof enough?
I'd quickly dismissed the thought of putting some heavy grease over the seals to make a temporary seal until I can have it fixed, but thought that might cause more problems.
 
I've never heard of that motor oil on seal idea, but who knows. I definitely would make sure it's a shaft seal before messing with them. At the very least, perform the starting fluid test again, as carefully as you can. Heavy grease or motor oil on shaft seal ends won't hurt anything.
Replacing the left side seal or seals is no big deal, but replacing the right side seals is another matter. Mine is a minority opinion, but I think the round throttle plates are best left undisturbed, and you need to remove them to get to the right-side seals, so make absolutely sure you need to replace them.
If you do buy shaft seals, Yamaha branded ones are what you should use, from Partzilla or any other on-line supply house, part # 256-14997-00.
I think you have multiple problems. A possible problem is that your advance rod needs lubricating and/or your advance springs are weak. That's easy to check and fix, so I'd start there.
After vacuum leaks and advance rod, I'd make sure carbs are synced, and air-mix screw is adjusted, and then I'd re-jet.
 
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I'll double check tomorrow. I wasn't exactly thorough as I didn't take the tank off and spray anywhere between the carbs, but I was precise with a quick spray in various spots including directly on the end of the throttle shaft on the right side of the right cylinder carb which directly increased the idle.

What's so tricky about the right side seals? I haven't seen a whole lot of info on replacing them, but it seems like a common issue with bikes of this age.
 
CaptCardboard said:
What's so tricky about the right side seals?
Click to expand...
With them being "linked" carbs, the inboard end of the throttle shafts have a bracket permanently fixed to the end of the shaft. That means you have to pull the shaft out to replace the seals. That involves removing the butterfly valve running through the shaft. First tricky bit... the shafts are actually pretty soft, so you're running the risk of bending it if you're a little too ham fisted. The screws holding the butterflys are bradded on the end, so it's a running fight getting 'em out. It calls for lots of finesse and patience.

But.... it's doable. Lots of info here to help "when" you do it.
 
CaptCardboard said:
I was precise with a quick spray in various spots including directly on the end of the throttle shaft on the right side of the right cylinder carb which directly increased the idle.
Click to expand...
Not an expert on this, but I'd think spraying starting fluid on an intake leak would bog the engine, causing idle to decrease.
When you have an unusual high idle due to a vacuum leak, I'm pretty sure spraying starting fluid on the vacuum leak will cause the high idle to decrease.
 
DogBunny said:
Not an expert on this, but I'd think spraying starting fluid on an intake leak would bog the engine, causing idle to decrease.
When you have an unusual high idle due to a vacuum leak, I'm pretty sure spraying starting fluid on the vacuum leak will cause the high idle to decrease.
Click to expand...
If you have an intake leak, then your mixture is lean... it's getting/sucking too much air. When you spray starting fluid (or any suitably flammable spray. I use electronic spray cleaner) and it gets sucked into the air leak, it richens the mixture, bringing it closer to correct. That causes an increase in rpm.
 
Jim said:
...you're a little too ham fisted...
Click to expand...

This is the abbreviated story of my existence.

I suppose I'll be more thorough with my can of starting fluid and make sure I know where any and all leaks are before I order any parts.
I'm not afraid of spending some time and being careful with my work, but I don't want to waste my time on a fools errand if a set of VM34s from 650central would solve the problem.

I'm a little motivated to do it sooner than later since it's starting to get warmer here. I know running lean means running hot, and overheating would be unfun.
 
Haven’t even owned starting fluid since many years ago, (Chevy small block days)
I wouldn’t even consider spraying that at throttle seals which are suspected to be leaking.
Reading of people using carburetor cleaner etcc on the Mikuni CV carburetors scares me. Too many problems on the forum with seals, o rings, diaphrams.
I only use oil on the shafts because that can actually improve the situation.
And by chance, today I did replace the right side throttle shaft. Those are chrome plated bronze.
The butterflies do require “finesse” to position and the whole reassembly of the linked carbs requires thought, care, and process to end up with everything aligned properly for things like the choke shaft to move freely.
I oiled everything.
IMG_7435.jpeg
 
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XSTime said:
Haven’t even owned starting fluid since many years ago, (Chevy small block days)
I wouldn’t even consider spraying that at throttle seals which are suspected to be leaking.
Reading of people using carburetor cleaner etcc on the Mikuni CV carburetors scares me. Too many problems on the forum with seals, o rings, diaphrams.
I only use oil on the shafts because that can actually improve the situation.
And by chance, today I did replace the right side throttle shaft. Those are chrome plated bronze.
The butterflies do require “finesse” to position and the whole reassembly of the linked carbs requires thought, care, and process to end up with everything aligned properly for things like the choke shaft to move freely.
I oiled everything.
View attachment 329317
Click to expand...
Nice work.
 
Wingedwheel said:
Actually it’s been posted that the Suzuki seals work as well and are cheaper.
https://www.partzilla.com/product/suzuki/13651-51010
Actually the first time I replaced them it wasn’t as hard as I thought. I did have to drill out one buggered screw but that turned out ok.
Click to expand...
Yes replacing seals is a big deal.
I've seen a fair number of carb sets that were dead of hamfisted attempted seal replacement. Most are (correctly) scared off by the complexity, delicate nature, of messing with the butterflies. Even after the screws are out getting the butterfly out of the shaft is tricky (easy to damage them) If you have a methodical, precise nature and are willing spend a couple DAYS doing a rebuild it's not impossible.
A possible kludge fix below, I've never done this, cuz well I can (and have friends that) do full carb overhauls. Once the seals are leaking (normal) they'll never be a "great" ride, tolerable is as close as you'll get.
so a kludge idea;
oil of wintergreen, to soften the seals.
then silicone (or other heavy body lube} thinned in solvent to allow it into the seals through the small cracks between parts.
the lube needs to follow the oil of wintergreen fairly quickly minutes maybe an hour not a day cuz it ( https://en.wikipedia.org/wiki/Methyl_salicylate )
softens rubber but when it evaporates the rubber will reharden, unless you get some lube to it.
droppers spray straws to direct the fluids where needs with motor idling (to suck them in) would be the idea. It might need repeating a time or two.
The thing is; EVERY set of these carbs I've done had rock hard no longer effective shaft seals. If the carbs aren't worn out the effect isn't huge but in dry dirty environments the shafts wear out the body bushings, causing big air leaks. "Game over"
I add lube to the seal cavities when reassembling and have contemplated adding small drilled holes to enable periodic lubing.
Whew that's all i got!
 
Something I got wrong earlier.
This assumes the OP has 1975 carbs, which his pic in post #1 indicates.
Your carbs are not linked. So, the outboard seal on each carb will be the easy one to replace. That would ne the the right shaft seal on the right carb, and the left shaft seal on the left carb.
The inboard seal on each carb is the one that will require removing the butterfly and shaft to get to. My minority opinion is not to do this unless you absolutely have to.
You say that spraying starting fluid on one of the outboard shaft seals changed your rpms. Replace that seal.
 
Woof. You guys have supplied me with some awesome information to consider. I didn't expect replacing shaft seals to be such an involved process.
My bike is a '75, but my carbs are linked, which sounds like making the offending seal a real bitch to replace.
I am intrigued by gggGary's suggestion of wintergreen oil and silicone. A more thoughtful way of caking thick oil around the seals like I'd mentioned earlier. I'm going to give this a shot first, but I'm beginning to feel a replacement set of carbs is a safer bet.
 
gggGary said:
The thing is; EVERY set of these carbs I've done had rock hard no longer effective shaft seals. If the carbs aren't worn out the effect isn't huge but in dry dirty environments the shafts wear out the body bushings, causing big air leaks. "Game over"
Click to expand...
nod yes GIF by Sleep On It
Yup! What he said. Personally I think all old carburetors need to be completely torn apart, thoroughly cleaned and have the seals and gaskets replaced, if you want them to work like they’re supposed to. Plugged jets and air leaks are a constant headache otherwise.
 
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