Per the chief mechanic for the Praga factory racing team, the proper chain length is anything that results in the engine being between the two short tubes connecting the parellal longitudinal chassis bars in the engine mounting area. So long as you are between those tubes, chain length will depend on where you want to place the engine for balance purposes (which is driver dependent).
This advice was for a Praga Dragon with an X30, but it should be sound for any chassis/engine combo.
paul, most standard #219 chain lengths are 114 links, although it depends where you want the engine positioned on the rails and what combination of front driver 10t or 11t and the rear gear. you can purchase a standard 114 link and try it on your kart, if you think it’s too long you can remove a link or two with a chain breaker. I’ve used 110, 112, 114 links before.
I think chain length is pretty much determined by the track. My rule of thumb is to use the shortest length that you can get by with. Less rotating mass and also not quite as easy to throw the chain when it set up as short as possible.