Need help with Z1B carbs

OK - I will try to make my saga brief. I have a 75 Z1B 900 and have been having trouble with it being rich at idle and low throttle/load. So i'm pretty confident it is something in the pilot circuit. Here's more details:
- paper element with stock air box
- 17.5 pilot jet, proper needle, clip at 2nd notch from top as in manual
- floats set ~3.5mm below flange using clear tube. Proper floats in all carbs
- float needles seem to seat fine, will not pass air when i blow on the inlets
- checked valve clearance and compression. Compression is 125-140, valve clearance is good.
- dyna ignition and coils, ignition all new. WG 12V relay mod. I have spark like crazy.
- carbs have been cleaned, air circuit will flow air fine.
- bike runs good at higher throttle openings and loads. will not idle smooth (idle set to ~1200-1300) and chucks at low throttle openings.
- opening air screws to 3 turns out does not seem to help
- plugs are sooty

I'm wondering if:
1) choke plungers are not sealing up. I pulled those today and the rubber on the bottom is pretty hard.
2) Needle or needle jets are worn, letting too much fuel in.

When i pulled the carbs today, i noticed fuel sitting in the #3 rubber intake boot.

Any ideas? I'm not sure what else to try other than trying to find a new set of carbs or sending these out somewhere to have them gone through.

Did you vacuum sync the carbs? If not, that's the first thing I'd do. If you haven't renewed all the internal rubber O-rings I'd do that just to be safe too.

Could your pilot jets be worn or could someone have changed them with Chinese "rebuild kit" parts?

I doubt the problem relates to the choke.

I have not vacuum synced, just bench synced. I can't tell if the needle jets are worn. The needles appear original and have some wear and surface corrosion on about 1/2" of the tip. While I've got these apart maybe I should replace them. How do the needle jets come out, are they pressed in?

Hi hydroscott,
They are pressed in. Takes lots of miles to wear a needle jet. We'd be more concerned with the corrosion you speak of having damaged the needle jets.

Are you sure the enrichener plungers are seating completely? There should be a tiny gap between the top tip of the plunger opener forks and the bottom of the upper rim of the double-ended nylon plunger washer when the choke lever is down.


Good Ridin'
slmjim & Z1BEBE

Yes the plungers do have clearance to the lifting tab so they are seated. I wonder about the rubber seal on the bottom, it seems to be very hard, but not obviously cracked or falling apart. I'll see about trying to get a closer look at the needle jets to see if there is obvious wear and otherwise will order some oem needles if I can find them. Thanks for the feedback.