Kz1000ltd running rich? Help needed

cartal wrote:

Additional question: these spark plugs are brand new. Can they be cleaned and reused?

Yes! Just heat the end with a blowtorch until the electrodes glow cherry red .
This will clean off all contaminants etc and simulates the conditions the plug experiences in the cylinder under normal running conditions.

I have seen these black sooty plugs myself when not renewing the choke plungers = No way to accurately tune the carb jetting.

A air cooled carb engine at HOT idle should be around 12.5:1 AFR (remember you can't run perfect 14.7 AFR EFI numbers on a air cooled carb engine) Outside temperature and engine temp have a lot to do with the numbers, as does air flow.

At 14:1 it was too cold out (no idea where you are) or the engine was cold and running lean not rich, the plugs are rich because the choke was on or the choke plungers leaking.

When you idle with leaking plungers the plugs will always be black, when it warms up and the engine starts burning properly (on "the ride") the soot will burn off at higher RPM and increased fueling. On the ride back you will slow down in traffic and idle into the garage causing the plugs to become black again! With this issue you will never know if your jetting is in the correct range for your engines state of tune.

If plugs are sooty black after 5 minutes there is extra fuel or no compression. Also note it takes a long time for plugs to go "tan", several heat cycles and much more than 5 minutes running.

All of this assumes you have good idle ignition timing (not advanced) and good hot compression numbers.
 

Reporting back with new main and pilot jets. So with the new 122,5 (main) and 37,5 (pilot jet), I think I have gone 180 degrees in the lean way. Now:

- Difficult to start
- Does not accelerate cleanly from idle, but bogs a bit and then catches up
- Absolutely clean plugs (no soot, nothing)
- Idle is a bit erratic
- Gets completely hang around 3000 rpm
- When running, gets explosions on retentions, some explosions when starting as well

I have tried to adjust pilot screws to enrichen it, going to 3 turns open, and it runs a bit better, but still same simptoms. 

Question: Would the pilot jet have such a huge impact? I'm thinking that the larger pilot jet would help with the idle acceleration bog, and enrich everything

Thougthts?

Cheers

Video for illustration 

The pilot carb circuit controls good engine running at idle.  Normal range for a pilot jet is between 1 and 2 turns out.  If you are going more than 2 it means your pilot jets are too small.  Try one size larger.  Conversely, if you are less than one turn out your pilot jets are too large and you should go one size smaller.

Yes! This is exactly what I just did, and the bike starts and idles perfectly again. I will not be able to try it until Friday, but sounds really nice again, and after 5
minutes of stationary running one plug (only had time to look at one!), looks pretty good

thank you!

One thing i learned about the kz engine is that it sot the plugs superfast when using the choke.I bought my kz august 2023 and it sotted the plugs fast if i had to use choke when starting up cold and i always had to use choke .I tried to do alot of fine adjustments on the mixturescrews .but that did not help because the soting of the plugs came from using choke even after 30 secounds .
Then next winter i rebuildt the engine and carbs like you have done.  I started riding the bike again in march and the outside temps was cold like 3 to 10 celsius.
and i had to use choke to get it started.  I shut the choke off as fast i can after starting with choke to minimize soting of the plugs. This summer i have done very very many small adjustments to the mixturescrews and checking the sparkplugs  to get it running best as possible.
One thing i learnt is that i always have to use the choke at cold starts.but then try to lower the choke much as possible after some seconds and then shut it of.
that minimizes the sotting. The sotting is not a problem because when riding it a little hard and at high revs will clean the plugs. so you should give it a good hard ride
maybe like Swest recomend  ride the piss.....and check the plugs after that and you will see the plugs look much cleaner. A bonus is that the pistonrings will also bead in fast . But carful on those first rides so you dont overheat your new rebuildt engine let it cool down  taking 10 minutes brakes.
By the way as zed1015 mention it can maybe come from hardened chokeplunger rubbers .I think maybe some of the startup sooting on my bike can have something to do with that too. so zed1015 im interested buying some choke plugers from you .
buttom line is:  the sot on plugs can be minimized by turning the choke off fast and ride the bike right away .and if the plugs sot down they will clean up riding the bike a little hard with high rews .

An i almost forgot to tell that my plugs sot less after switching from ngk  to Denso plugs denso  W24ES-U