Carbonized spark plugs

Hello there, just got out my motorcycle yesterday. But I knew for sure it was ready for a tune-up since last year it was really rough and a little bit rich on gas. It's an Fz600 1988

So, Ive got a problem my spark plugs (all four) get carbonised afther only an hour and then, no fire (duh!).

Here is what I already did:

-Cleaned carbs, they are now clean. Everything seems fine

- Balanced carbs, my idle is now better at low temps (they needed it!)

- Removed air bowl and filter, still runs rich (I'll put it back later)

- Adjusted a float height of 1mm but it was still on the specs before, juste made sure it was really precise.

I'm now searching for a fuel level prolem in the carbs, adjusted a float of 1mm but I doubt that was it. So anybody has a good and comprehensive procedure to adjust fuel level in carbs ? Or even better, any suggestions on what the problem might be?

BeerBaron