Of the barrels? Left sitting on side stand with 2 spark plugs not done up properly, water has got in and caused a water mark.
Or, if it's the carbs, 2 slides are in the wrong way round,(edit....not possible, thinking about it more) or wrong slides fitted.
Edit.....again......I see now, definitely carbs not bores 🙄🙄🙄
Have 2 dropped down so far, you can't see the half moons?
Sorry about the above, been out on the bike all day, I didn't realize how knackered I was 😄😄😄