kz440 one cylinder firing?

Ok I got a 1982 kz440 for a few hundred dollars. It was sitting for some time but I am somewhat mechanically enclined and got it running in like 30 min.This is my first bike and im new at motorcycle repairs.I noticed that only the left side pipe was getting good and hot.So I pulled the plug on the right side and checked for spark and have a good blue flame.Reinstalled plug and pulled left side good flame there. Well when I pulled the right side and cranked it it fired up and ran.But when I pulled the left side it would not fire up.I put my hand at the exhaust and could feel detonation in the left side but just more of a air blow out of the right.

Can someone point me in the right direction to trouble shoot this issue.Could it be a timing issue,carb issue or what.

A good cleaning of the carbs,fuel tank,and fuel control valve on the tank(it's called a petcock) is the first thing followed by checking for compression in the cylinders and then valve clearances to see what you have and don't have.

thanks I will do all of that. I was planning on cleaning the carbs and Have a manual to check the valve clearances. Also not to be a pest but I have an oil leak on the left side coming out of the cover where the shift mechanism comes out of and it only leaks when the motor has run for a while. is there a oil seal on the shifter shaft or behind the sprocket.And can they be replaced with engine on the bike.Like are they snap ring seals I hope there not sanwiched in between the crank case halves.I see oil drips from the shift rob and it is dripping on the exhaust.