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After an obnoxiously long delay getting piston rings that fit, and losing my job looks like I'll have plenty of time to put this back together this week. First set of rings weren't the correct size / did not have the taper in the black ring.... Second set took forever to arrive but was also incorrect, thankfully the seller realized they sent the wrong rings and express mailed the right ones. Can't imagine how some of you do this with even older bikes where parts are even harder to find! 

Its a race to the finish...you started first and looks like you'll finish first.

I found Berryman's Chem Dip to be the most effective at loosening the old gasket but its still a miserable tedious and time-consuming chore. I found that laying some paper towels down on the gasket and then soaking them for a while worked best but it still sucked. Just yesterday I found some generic (Essential Everyday) green scotch brite type pads that work so well I'm a bit wary of them possibly being too good. But I'm using them anyway.

Well the other day I finished getting it all put back together and fired up - she's alive! Today I did some more fine tuning and also had to Frankenstein together a petcock* but it officially has risen its first road mile in 15 years! Rowed up through gears up to about 45mph happily without hesitation or backfiring that I noticed. 
Having a small victory splash of whiskey and then going to tinker a bit more. 

Anyone have any idea why at idle (cold or warm) it wants to stumble and die as soon as I give it any throttle? I feel like I remember reading about it being an issue with the pilot system... 
OH an annoyingly the seat no does not lock into place? 

*Petcock rebuild kit I got was garbage, fortunately had another original petcock laying around from a 650, was able to use a combo of parts from each to put together one that didn't leak at ON and also flowed when under vacuum. 

Update: seat latch is fixed. Probably from precious owner slamming it to try to close it, they bent the mechanism inside the lock slightly so it was sticking. Cleaned it, lubed it, used 400g sandpaper to file it down to fit, works like a charm. 

Set pilot screws (US model) to 2.5 turns out and then tinkered with it a bit as I was experiencing the idle problem described above. Warmed the bike up well at idle and took it for a 6 mile ride. It did great! 
Now near the end of the ride, last stop sign before the driveway, I come to a near full stop and the engine almost dies. I catch it, make it home, get to the garage door and it dies. Get off the bike to discover the right side carb bowl is absolutely PISSING fuel for no obvious reason. Screw was tight, o ring was in good shape, I just replaced these. Threw in a spare from another set of carbs, no problem.... This thing has serious gremlins. 

good to hear she's running again. I hope mine is soon. Then if I am so lucky, I also expect pesky carb issues that are aggravating but don't stop it from running.

Well, that was short lived. Never checked the float levels and it seems one was set too high, and also the float needle stuck open, so I'm guessing that somehow flooded the engine? Anywho gas got in the oil, so out with the old, hand spun the engine to get as much out as I could, and in with fresh. Reset float levels to about 5.5mm, which was a pain in the ass, reset pilot screws to 2.75 turns out but haven't tried to fire it yet. 

Horn is busted, trying to refurb it before replacing - armature inside is corroded but moves, just not well. Horn will buzz and diaphragm moves but doesn't sound. For the 8 dollar generic replacement I may just go that route or splurge on a 12 dollar snail. 

Taking a week off to see family but hopefully then I'll be back, finish the mechanics then it's onto aesthetics for some minor paint and detail work!

Do yourself a favor and go through the carbs completely, if you haven't already, before attempting to fire up the bike.  Nothing worse than going back to the start when you think you are almost done.  The pilot circuits love to plug up, which requires removing the pilot screw, pilot jets, and any jet nozzle that may be present in the system in order to make sure they are open and clear.

If the float needle stuck open, that needs to be remedied, or this will all happen again. There are no shortcuts to carb cleaning. 

Yep already did a full rebuild on the carbs. Full dismantle and soaked in parts cleaner, cleaned per the service manual and blown out with air. That's why I was so surprised by the stuck float valve as it was brand new...must have been defective? 
I think I finally got the petcock to stop leaking - same thing brand new rebuild and full clean and it immediately leaked even when in the On position. 

Was it an aftermarket float valve?

I suppose - I got it from a seller out of Japan so I figured it would have been at least halfway decent. Z1 was out of stock for months when I was searching 

Could also be a small bit of rust or dirt. Do you have a high quality filter in place?