The rusty hulk

Needle od is correct .099"
Jet needle .105" (perhaps .107")
Main jet is correct .044"
Cylinder #1 way to rich, suspected plunger, not sure now, something not right.

Mmmm.... brain fart talking about the '75 carbs.

Assuming correct fuel level, swap plungers & see if the problem follows the plunger.

Good Ridin'
slmjim & Z1BEBE

I swapped plungers, #1 stayed very rich.
Disassembled carb #1 and measured parts with rods and micrometer.
Needle jet is .117" (.002" over size) other parts correct size.
I disassembled two more carbs this morning, needle jets are .115"
Hard to believe .002" has the effect I see.

Yeah, .002 doesn't sound like enough to richen the mix by much. Of one was a real glutton for punishment, needle jets could be pressed out of another carb & swapped.

Voltage drop (usually through the ignition switch) at the coil primary can cause plug fouling, but that should manifest on all plugs. Is full battery voltage available at the coil primaries?

This might be a longshot, and will only work if you have the OEM clear tube fuel level tool or something similar for early Z1 carbs with the 17mm plugs:
With the carbs on the engine, install the tube tool on the suspect carb & secure the tube such that it can be easily seen & won't dump fuel. Start the bike & observe if vibration causes fuel level to rise above spec. If so, needle valve and/or seat might be suspect. Otherwise, we got nuthin' :huh: .

Good Ridin'
slmjim & Z1BEBE

Needle jets will wear over time due to the action of the needle on the downstream side of the jet. (It rubs.) This is a recommended check point in the Kawasaki carburetor training manual. It's one of the few wear parts in the carbs, and yes, a 0.002" gap will make a hell of a difference to fuel flow.

What about the needle? Is it a 5J9? It's important that the correct needle is used to provide the correct fuel flow. Maybe someone changed out that needle and replaced with something else?

One of my 2 strokes had an issue running rich, like hardrockminer said, the needle jet was worn. From research, they wear oval. Not a replacement part for me so I had to buy a new carb.

Thanks for the comments.
#1 plug is tan with spare carb.
Currently have air screw at 2.5 turns out to lean mix, still very rich.
Ordered some needle jets, will report when they arrive.
I've owned ten of these, never seen this before.

The rusty hulk, version 2020

Hang on and don’t blink. The last one was over quickly.:woohoo:

>>> "Hang on and don’t blink. The last one was over quickly"
Working on Z1, H1, H2 at same time.
Wow, what a pile of parts !

Anyone seen this ?