Put weight on my Mexican black king snake

Hi i recently bought a Mexican black king snake, hes around 5 years old and around 5ft long. but hes really skinny it looks like his previous owner wasn't feeding him much. Iv looked online at various king snakes and mine is half the size!
i wanted to ask people for there advice because I don't want to throw loads of mice at him and make him ill. At the moment iv been feeding 2 large mice a week but im sure he would eat more if i give them to him.

thanks for reading
josh

How much does it weigh?

Here is a chart I found for Corns, I think it's probably appropriate for Kings:

http://repticake.ucoz.com/load/corn_..._chart/1-1-0-7

My two year old four foot female MBK is a garbage gut and would eat until she bursts. She gets a jumbo mouse every five days.

Focus on putting the weight back on him slowly. Get a scale and weigh him about once a month. Two large mice weekly should be fine, but if you don't see him picking up weight and getting a better body shape, then schedule a vet visit and take in a fecal sample to test for parasites.

his weight is 580g, thanks for your advice

I just looked and on average they are 1800g/2200g fully grown

so 580g is mega bad