I have been searching all over the internet and here with no real answers. I just got my bare gsr head back from my machine shop after a hot tank, re surface, and valve job, and there is still some carbon build up inside the head. Is this common or should I be taking it back to them? I was expecting all carbon to be gone.

Also, not sure if this is the right section or not.

 

quick cell phone pics, you can see how some of it flaked off in these pictures, but can still see thick build up by the bottom of the valve guides.

one that isn't so bad
https://www.dropbox.com/s/3j29af5fe6...2023.15.11.jpg
one of the worse ones
https://www.dropbox.com/s/5yg7wf4bzv...2023.14.32.jpg

 

Looks like a shitty hot tank job. BUT, there is some build up that has to be scraped out, that no amount of hot tanking will remove. Your head may be such a case.