1978 KZ100D Z!R Project

TexasKZ wrote: I do see how a bubble could get trapped between the seals, but I cannot even imagine how that would make a soft lever, or one that travels too far, since the pressure is supposed to build down stream of the primary cup.

The air would presumably move from the center chamber to the pressure chamber during the same time that fluid moves from the center chamber to the pressure chamber, past the seal on the return stroke during pressure bleeding operations.

Wow, what a great discussion. Thanks to everyone for contributing. I have a lot better understanding now.
What I did: Removed the MC and disassembled. Kicked myself for discarding the original piston. Acquired a second MC from the donor of the bike. It was frozen solid. Tried freeing it with penetrating oil, no good. Soaked it in Evaporust for 2 days, scrubbed it with soap and hot water. Repeated penetrating oil, with success. Compared the OEM and K&L pistons, visually and measuring with vernier caliper. They were within a few hundredths of a mm of each other. According to the specs in a Kaw. service manual, both pistons were slightly undersize, and the rubber cups barely large enough. Took a comparison pic exactly like DOHC's. Came to the conclusion that the Z1R MC is just a bitch to bleed, and the K&L piston was not the problem. But I did use my friend's MC with its OEM piston and seals, which looked great after cleaning. Its long, frozen slumber did not appear to have harmed it.
I repeated the vacuum bleeding process. This time I dismounted the calipers and pushed the pistons back by hand. A little air bubbled into the reservoir. I remounted them and continued and began to get a firm lever. I quit for the day since I was tired, forgetting the tying off the lever trick. The next day, my mechanic friend said that trick only needs a couple hours to work. I did a little more vac. bleeding, which made further improvement, then tied the lever back for about 3 hours. It did help, but not dramatically. I now have a nice firm lever, yay!
One slight problem remains. With both calipers torqued in place, observing closely while pumping the lever, one glides evenly back and forth, but the other kind of wiggles, like it's hanging up a little on one of the bolts. I did polish slight corrosion off all the bolts and grease them and the o-rings and dust covers lightly.
Not a big worry. I bet the issue will resolve itself with some mileage.
Let me offer this for opinions: The design of the Z1R MC is odd, with a "dead zone" of cylinder beyond the outlets. Usually, a cylinder dumps out a single outlet on the back wall. This one has 2 outlets in the side wall, before the end. My theory is that air can get trapped there, beyond the outlets.
Another reason for bleeding woes, in my case. The bike was locked in a straight upright position on a lift table. I think being able to tilt the bike so the "dead zone" was lower than the outlets may have prevented air from collecting there. Or, I could be full of it. Your opinion?
BTW, I was tapping with a wrench on the MC and calipers during the bleeding process to help dislodge bubbles. Waste of time?
Thanks again.

Last week I removed the old seat cover, thinking I would have the new one on the same day. Wrong! The old cover hid moderate rust on the front of the pan, with a small perforation and the front edge was really jagged. I cut it back with a cutting wheel, leaving only about a 2 inch section of the original edge. The rest was smooth, but a little uneven. The rest of the pan's perimeter was undamaged, just a few of the "shark teeth" were broken. I tried to cut a new one into the front with a dremel, but it was kinda sloppy, but functional. The other 2 places where it really needed something, I just drilled a hole for a sheetmetal screw. I don't have a sandblast cabinet, so I soaked the pan with Evaporust for a couple days, then sealed it with Bulldog adhesion promoter, then primed and painted. Looked pretty good, considering, but I'd gladly have paid $200 for an NOS pan. I found an almost identical replacement for the trim that goes over the bottom edge of the pan. For the front edge, I used a heavier vinyl edge trim with a steel core that restored the straightness.
As for the foam, I'd have replaced it with NOS, too, but like the pan, unobtanium. I used duct tape to reinforce the thin parts. Fortunately, the seat top was in good shape. At the last minute I decided to add a thin layer (1/8") of foam I had leftover from a car door panel job. Glad I did. When fitting the cover, it seemed it might have been a little loose without it. I was very happy with how the cover fit, very snug, even with a couple of the shark teeth missing and the mods I had to do.
When I placed the seat on the bike, I was unhappy with how it fit over the rear cowl. The side to side profile is rounded, whereas the cowl is more square. The worn paint on the top corners of the cowl tell me this is not a new condition, and the pan didn't look damaged in that area. You'd have to have tremendous hand strength to "square off" the contour of the steel pan. TBC.
panel job.

Where did you get the replacement trim for the edge of the pan

Hey Greg,
Space Age Paint in Mesa. They have a website. The small trim was .65/foot, and it's door edge trim, # DG150B12. (that's a b, not an Don't know who makes it, You'll need 7ft.
We got the bike running today. Had to take the carbs off again, #4 needle valve was stuck closed. Just a little smoky, hopefully from sitting. I rode it around the block. Felt great, but the brake pads need to get bedded in. Little oil leak by the pressure switch. And I got the hi and low beams backwards, duh. Need to fix that and get the bodywork back on. And the speedo drive. Little stuff. Got to get legal so I can ride it now!

Update:
Jetting story. I have Mikuni BS34 (police bike) carbs, K&N pods, and 4-1 headers. The carbs did have Dynojet needles (Position 1, top), and appeared to have the main air jet and slide lift holes enlarged. But they had Mikuni 120 jets. The bike ran great up to about 5k, then lost power. I moved the E-clip down to the 3rd (middle) position. Much improved, but still needing fuel.
I got new Dynojet #134 jets, and moved the clips up to #2 postion. This is very workable: nice start, idle, good power to redline. DJet recommends 138's , but I'll use this setup for awhile, and check the plugs. I guess I could've left the needles at 3 with similar results.
Speedo now working. Found that a 1979 KZ400 B2 has the same p/n drive unit. Got one, supposedly from a 78 KZ400, for $30. Took 4 months to find. Cleaned, regreased, put in new seal.
Now I'm ready to rack up some miles!