hellow 

i want mi custome block to catch fire as if it was some wood block 
not the kind of furnace fuel 
but the kind of catch fire whit flint and steel 

i sont get it 
it must be put in some of those json files ?

or its a function flag that needs to be added to the block code ?

in your block class, override getFireSpreadSpeed  and getFlammability.

try just returning 5 and 20 and see how it works for you.