Since head is off, seafoam, or gas. Scotch bright pad

Break clean too

Brake/carb cleaner

Thanks, but it is not moving with just sprays. It might need some force. I don't know if a scotch bright pad will do it either. I *might* need to get more abrasive but don't know how abrasive is too much.

You could try any of the above mentioned fuilds, just let it setup for a short time then try to remove it.

I had an old l28et from a 280z, the pistons had this nasty black build up that wouldn't come of no matter what I sprayed on it. I let some c16 set in the cylinders with a cap on top for a few hours and it cleaned right up.

Ok thanks again everyone. I'll try and just be patient with it.

I'd use some Mopar CCC with a nylon bristled brush

I love to use seafoam, just let it soak for a few hours and the stuff brushes right off with a toothbrush. Carbon deposits, black gunk, it gets it all

1 inch knotted wire brush on a die grinder or drill and have at it.

make sure you wear safety glasses.

No you will not hurt the valve seats, since they are under the valve.

+1 for safety glasses. Cant tell you how many times they have saved my eyes