1981 KZ1100 running lean - carb questions

Recently acquired an 81 KZ1100 and trying to get the engine running right before I tackle anything else. First time getting into engine work so bear with me…

Engine was running on choke only, so pulled the carbs (Mikuni, stock carbs I think? Why is there no model number stamped on these…) and gave them a good cleaning – some debris in there but all orifices I can see are now cleared out. Re-installed and still the same issue. Only running on choke and running lean by the sound of it.

So pulled the carbs again and the engine-side boots. Some radial cracks on the flange side but not passing all the way through. Then I figured I should re-check the fuel mix screws while I had it off. Of course one of the screw heads broke off but thankfully just when I started to thread in. Was able to extract without drilling out but now I’m in a holding pattern til I get new screws. Figured I may’s well get some input on other checks or replacements to perform while I wait.

Other notes:
- Idle adjustment screw feels like it’s got resistance but doesn’t have much effect on idle
- Bench synced carbs and they were quite close to balanced
- Choke shaft plunger seals (like these: www.z1enterprises.com/choke-plunger-cap-...00-kz650-zn1100.html ) are all torn at least partially
- Sprayed carb cleaner around boots while idling on choke. Sounded like rev’s increased to me.
- Valve clearances okay, new spark plugs purchased to go in when reassembled

Next steps for me:
- Order new fuel mix screws
- Order new carb boots to be safe
- Possibly pull jets in carbs and check that they’re correct size. (Anybody know where to find correct sizing?)

Questions for you guys:
1. Those choke shaft plunger seals are just for dust right? They’re not the source of an air leak.
2. New fuel mix screws come with a spring – is this correct? (Manual shows this too.) None of the mix screws in my carbs have springs. Sure seems like this would affect the initial seated position.
3. Other places to check for leaks?
4. Other things to investigate while I’m waiting?

Appreciate any and all help. Thanks.

If you google "Mikuni Carb rebuild tutorial" there is a detailed guide on how to properly rebuild your set. You might want to go through it to see if you missed anything.

Typically when dealing with old carburetors of unknown history, the best bet is to completely disassemble them, yes, removed from the rack, and very carefully clean all the hard parts. The pilot circuit is oftent the culprit when the engine will not idle without the enrichner, or shows other signs of leanness. It is difficult to clean because the passages are so tiny.
All of the orings and gaskets should be replaced with new.
I am pretty sure that on the BS34s, the purpose of the mixture screw spring is to put pressure on the threads so that vibration will not cause the screw to back out.
The enrichner plunger dust cover is just as you wrote, to keep dirt and moisture out. I doubt if they are your problem, but replacing with new is a good idea.
Surface cracks on the carb holders are an indication that the rubber has shrunk and is losing elasticity. Air leaks are highly likely.
As Nessism pointed out, there are some good tutorials on YouTube .
Patience, thoroughness and fierce attention to detail will put the carburetors back in good condition.

Oh, and the factory jet sizes are listed in the factory service manual.

Just in case you do not already have one, here is a downloadable PDF copy --

www.kzrider.com/modules/ServiceManuals/K...Service%20Manual.pdf

Thanks gents.

I've read the detailed Mikuni tutorial. Will likely do another carb rebuild while I'm waiting for parts.

Good to know there's no major issues/components I need to investigate and remedy. Just the carbs and mounting for now...