1998 kawasaki vuclcan classic 1500 engine problem

I have a friends bike in my shop and am having problems with it. It sat up for a while and would not run. I charged the battery and removed and cleaned the carb. Bike now cranks and runs fair when it is cold but as soon as it warms up it starts back fireing through the carb with a lot of knocking and pinging until it will eventually die. Any ideas? I am by trade an aircraft mechanic and have worked on a lot of motorcycles mostly Harleys with a few hondas and yamahas but this is my first Kawasaki.