Spark plugs fouling

Hope you can help me.
I bought this Z 1300 with this problem:
After few kilometers all six spark plugs build up carbon.First i changed the float valves ,fuel level is 7-8 mm from the base edge of the carb body (as i read in some topics).Idle screws are about 3 and half out,set with colortune.
Change all coils and ht leads, sparks improved a lot.Chek ignition timing.
Cold starts produced a few of black smoke,then disappear. Cheking from the spark plug hole,the piston crown look as wet even with the engine very hot.
In the pic the spark after half hour( from new)
Any advice would be apreciated
thank
Fabio

OK,

Could Be...............

Burning oil via valve stem oil seals or piston rings.
Poor Compression.
Float Valves allowing fuel past .
O Rings on Float Valve Buckets allowing fuel past (hard and perished)
Chokes not fully closing or not seating properly.
Valve timing slightly out, engine will still run with this......

Outer Ring of spark plug looks lean, which is main jet reading, but Centre Strap looks very dirty, which is Pilot / Mixture reading. Did you set mixtures at the centre point between YELLOW RICH and WHITE LEAN ????...........The best BUNSEN Blue colour you can achieve !
If pistons crowns are wet when engine is hot then it can only be excess fuel or oil.

If I had to make a guess, I would say its incorrect petrol supply or burning oil...............or both !

Pete F
UK

I tend to agree with Strate6 here.
I see in the picture, the overhead light reflecting on the center electrode so it's definitely wet and unless it was just pulled out of the engine and the cylinder was dead, then the wetness is oil. I'm sure if you smelled the plug, it would smell like engine oil.
If the plugs are BPR6es or BP6es, then the heat range is hot enough that the oil should have burnt off if the engine was running hot enough but since the residue is black, the engine is still running cold. This is likely due to the engine running rich with gas as well.

So, are the carb throttle barrels dropping as they should or are they hanging up? ( I believe your problem is with the Main circuit and not the Idle/Low Speed circuit since you have colortuned the carbs at idle.)
Have you confirmed that the main jet needles are in the middle adjustment slot?
The other thing that comes to mind- Have you inspected the enrichment valves on the side of the carbs? I know when I overhauled my carbs, the enrichment valves were seized in the carb body with white oxide from the Ethanol in the fuel absorbing water and oxidizing the aluminum of the carb. If they are stuck openor partially open, this could cause a rich mixture.

Thanks for the answers.
So i did some checks:
First i remove the airbox ,the throttle are almost fully closed,no fuel spill out from the needle jet at idle ,all is dry.
The fuel cosumtion (at idle 1100 rpm ) is 1.8 liter per hours,i have no idea if is ok or not.
All cilinder at idle are colortuned bunsen blue, change a little at half throttle,only one stay on yellow.
For the the enrichment valves : what about if i remove the internal valve (just in one carb) for try ?

Fabio

Fabio,

If I were you I would remove the carbs and give tham a full internal clean and fir new O-Rings, Float Valves etc.....if required.
Then set the mixtures and sync's.

You then know the carbs are ok and can go looking from there.

Pete F
UK

3 questions:
1) How many miles on the bike?
2) What exhaust system is being used ?
3) Has the air-injection been disabled?