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........
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?