1980 550e cylinder intermittent

[Trolleywire]

Hi, ok so been a while so I thought I’d post a new thread. Cleaned carbs, brand new coils, new spark plugs. Valves in spec, Charged up battery. It started up, ran with the choke on but died once up to temperature and pushed choke in. Everything is stock including airbox. I heard a cylinder come on and off (fire up, turn off) then stopped and it was running on only 3 as I’m sure that’s why it won’t idle or start properly back up if only three are firing. So, I guess I will have to isolate which cylinder it is and find out why it’s not getting fuel. It’s not spark as everything is new. Could it be a sticking needle valve? Not getting fuel? I also think the vacuum petcock it not operating properly as it will run on prime but not on. But it could be low on fuel as it was revving up once switched to prime. Any thoughts? Thx.

[Nessism]

Maybe poor spark. Check the spark plug boots and consider removing them and cutting back the spark plug lead by 3/8" or so and screwing the caps back on. And needless to say, check the plugs and/or replace them.