Cylinder missing

Where would you guys suggest i start to locate reason one cylinder doesn't fire until running and working a few minutes 318 engine in 9ud6??

Most likely a stuck exhaust valve. Carbon can get up in around worn valves and guides and make them stick when cold.

Need to do some diagnostics. Crack lines loose until you know which hole it is. Then swap injector with known good hole. if the miss follows it is injector. If not then it is a good chance it is just slightly lower compression. Give it a small sniff of ether. If it picks the hole up for a bit then it is lower compression. If not then it is looking like hard parts. Possible valve issue or worn rings. They will run a long time like that. Been running a #12 like that for 9 yrs. Hardly notice in the summer. Needs a couple small sniffs to build heat in that hole in the winter. Once it starts firing it will keep firing on it.