Ya I think they'll be an improvement Bob....lol.

I don't know gggGary, Never really paid that much attention to them whenever I had the carbs off, but no wonder there was an air leak. I am interested in pulling the used replacement set that is also leaking on the right side to see what's up with them. No signs of leaks on my other project, the 78E, but haven't run it for awhile and didn't spray any carb cleaner at it. Need to do that.
 
Come to think of it, there WAS a glaring omission in this thread:

"Chronic complaints about carb pulls and installs".

Having all them cracks must've made it easy...
 
TwoMany - you are an amazing resource for this forum: unbelievably knowledgeable, endlessly patient, relentlessly thorough and invariably kind to everyone.

Thank you.

Pete

PS.....any chance you could make it to the upcoming....awwwww, forget it. Fredericksburg Texas is a loooong way from Detroit I guess.
 
I think your multiple carb removals and installs put most of those cracks in there. I've never seen one split as badly as that one. Spraying with carb cleaner to check for leaks probably didn't help matters either. That stuff is tough on rubber. I use something milder like WD40. It may not as readily show leaks but it doesn't hurt the rubber much either. A technique I've heard of but not tried is using an UNLIT propane torch. Poke the end in all around the manifold with the gas on. Sounds like a feasible test.
 
Speaking of cracked, found one on RH period piece intake, wasn't happy with how it was starting. Could see it backfiring (sound and the carbs jump a bit). Saw a tiny yellow flash repeatedly between the fingers at the top of the steel intake cover and clamp, some ether verified it. Carbs are back off, hopefully the last time for a while.
 
Wow, been a lot happen here today. Had an unexpected day off and spent it in my shop.

I always check in on things throughout the day when I'm working, but not so much when I'm working on my bikes. Damn kids and they're phones when they're working eh?

Nothing else important to say, except,

This is finally my 10,000th post!

That's all.
Just wanted to put it in robinc's thread...

Wow 2M, that is no hijack. Congratulations and a well deserved accomplishment with nary a wasted word!

I am honored and humbled. You are a foundational, invaluable, member of this forum that has helped shape it into the amazing resource that it is.

You continue to inspire me and stretch me to do more, learn more, and ask those questions: "Why is it doing that?", "How does it do that", "What should it be doing?"

Thank you.
 
I think your multiple carb removals and installs put most of those cracks in there. I've never seen one split as badly as that one.

LOL, ya you're probably right 5twins. Sometimes the best lessons are the ones learned the hard way. I think they had been leaking all along and I probably made them worse. I also use WD40, don't know why I kept grabbing the carb cleaner. Love the unlit propane idea, will do that in the future. Thanks for the tip.
 
I was going to wait until I had final good news and could say that I might be looking for membership in Bob's 'Cautiously Optimistic' club, but now I think an update today is appropriate.

I have been trying to go through the troubleshooting process one step at time, doing one thing at a time so I will know the results or lack thereof, with each change. Certainly takes longer but that way I'd know for sure.
Decided today that I was going to test these rebuilt carbs on my 78 and thereby confirm they're good or establish they're not. Nice to have a test bike kicking around, and it hasn't been run for almost a month anyways. Importantly this would also help confirm 5twins suspicion that the points are bad.

Pulled the old carbs. No griping here 2M, actually did it mostly with one hand, distracted while on a phone call. Could have closed my eyes I bet.

Installed the carbs from the 77 with Dielectric grease. Took a few kicks, but not too bad. I only have 1 motorcycle battery and didn't bother pulling it. Just jumped off my old trolling motor battery that doesn't have enough cranking amps to spin the starter.

I have not done a thing mechanically to this bike yet (maybe that's good news for it?). It ran so well if the brakes worked I would have had it around the block, carefully on those old tires. They look great just 12 or 13 years old. It's not running perfectly, a little miss here and there but boy am I excited about how good this girls gonna be.

Then, what's that squeaking? I pulled out Bob's famous 'hose-oscope' which Bob, is an amazing idea and an amazingly sensitive/accurate device.
Idling fine, but sounded like the right manifold was leaking. Couldn't believe another set of manifolds was bad so I started to more carefully place the 'scope'. Bob, I really wish you would get the instruction manual written and online.
Let's see if I might happen to have a carb pic........



Choke leak.jpg


I was listening along the carb side of the manifold and heard 'loud' squeaking all along and especially at the red arrow. Now, you can probably see where this is going. It was actually a choke housing leak that was being channeled in the semi circle around the throttle shaft housing and registering at the red arrow.

Bob, please pass me the Dope hat.

Now I have to ashamedly say, "My name is robinc. I am a carbaholic. And I have used Mikes/XS650Direct parts on carbs"

When I had tested and then rebuilt these I thought I was picking up on a choke leak. As we know those gaskets are no longer available from Yamaha so I did the unthinkable. I got some from XSD. You can almost see through them, but I thought what the hay......ya.

Off they come. Buddy was hanging out today. He did it blindfolded. Made my own gasket from Felpro gasket maker and installed it with Hylomar Blue. Back on bike, one of us on each side spinnin' wrenches, goes quick.

Fired up the old girl and it ran way better. Not as good as the Black but way better than it was. Some slight missing and stumble. No more crazy fluctuating idle but it did have a tendency to want to stall. So for a thick headed me I'm going to think the carbs must be OK, these manifolds and those on the black do seem to leak a bit but will now test them with a propane bottle.

So it’s been just over a week since ggGary brought up checking points and 5twins recommended just replacing them. I wasn’t ignoring this advice but wanted to chase down and absolutely rule out carb issues. 2M’s easy pilot circuit tests lead to discovering bad, leaking manifolds and then subsequently a choke gasket leak, so that was a good thing. So, points/timing are next on the list, then if required condenser, then who knows?

You might say I wasted a week by not just doing them then, but I rather like to think of it as an investment of time that will pay off now in Many ways.

Once again, thank you all for your help and encouragement.

Edit: Forgot to add this last night.

Have a looky at this Bob. Obviously part of the carb mold. This wasn't all that pronounced, but there, and a halfway decent thickness gasket would absorb it. I wonder how many different molds there were and how many of them had this? I don't know much about casting metals (built a small local foundry years ago for the old DGM - Dominion Gas Meter Co., so saw the process) and I wonder if this was a defect or a registration point of some sort?

Choke casting flash highlight.jpg
 
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All right Robin you are making steady progress here! Glad you tried and had success with that little "hose-oscope" method.
Regarding the casting surface under the enrichener, I was going to take a photograph later and post it. I just received a used carburetor body from Gary and that spot you had circled and if you look straight above it there is another small spot, those two spots appear in exactly the same location on the three carburetor bodies I have. It must've been caused by the casting process. I agree with you, that the original factory gaskets must've been thick enough to seal imperfections and the new very thin gaskets only highlight every flaw.
Glad you had a productive day, and keep on swinging.
Edit: here is my new carburetor body
IMG_5113.JPG
 
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My experience is in plastic injection and blow molding rather than metal casting - but the principles are the same.

I'm pretty sure these carb bodies are die castings using a high pressure process in which molten metal is squirted into a heavily built steel die or mold and then allowed to cool.

I may be all wet here but looking at Bob's photo, I would say that little the pimple on the sealing surface might be a gate - which is the part of a cast or injection moulded part where the molten material is pushed or poured into the mold. Gates usually look like a little bump sticking up or a little depression on the surface of the finished part. They are usually placed in some spot on the mold where there are no appearance issues and where leaks or stress risers aren't a big concern.

If you look in the very centre of the bottom of a margarine tub or large yoghurt container, there is usually a gate there and it looks a lot like that pimple on Bob's and Robin's carbs. Most of us built plastic models when we were kids and played with toys (not like now of course - we're men...but, I guess we still play with toys). If you recall the "tree" thingy on which the parts were mounted, the junction between the tree (or "sprue" to give it its proper name) and the actual model part - was a gate. You usually had to trim it off after breaking the part away from the sprue.

Anyhow, I must admit that putting a gate in the middle of an area which needs to be sealed for proper function of the carburetor seems like an odd choice, but then, I've never designed a carburetor, so what do I know.

Pete
 
Wow, you guys are good. Your detective sleuthing, zeroing-in on the imperfect casting surface, AND finding it replicated on other carb bodies, deserves a few "Attaboys"!

Reviewing some of my '71 carb pics shows the enrichner surface to be much flatter and smoother. I've also found some references that claim that the early 70-71 carbs came *without* enrichner gaskets. Those would've been casted by Solex, in Germany.

From what I've read, somewhere around '74 (?), the carb production transferred to Mikuni. New molds, new quality control, ...etc. The gaskets I've seen appear to be thick enuff to handle the flaws.

Myself, I'd cookup some sort of abrasive flattening/smoothing tool to attack that surface. Else, use sufficiently thick gasketing...
 
I wonder if it could be lapped on a piece of plate glass with some polishing compound...like AutoSol or even pumice-toothpaste or perhaps a piece of Emory cloth.
 
Ya, that would work Pete, the throttle shaft housing is a bit in the way though. Could use a piece of flat stock with some W/D paper or fine emery cloth adhesived to it.Tried 5twins idea of scraping it off with a small knife. Too stubborn. So I just carefully drew a small needle file over it, keeping it flat, a few pull passes and it was gone. As 2M says though, a thick enough gasket will absorb it. Don't know if that was the reason for my almost see through XSD (XSDrama) gasket to leak or if it was just too thin to seal.
 
I did the same thing, I have a very small, very fine flat file that I carefully worked over the raised bump to flatten it. I made this composite photo of the three carburetor bodies I have, check it out.
5D4B5BFF-4F0B-4125-9B7F-3EE553D193CF.jpg
 
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