Engine misses until warmed up ... Coil?

[40 Nuck]

I have a 1940 EL, and noticed that the engine would miss (as best I could tell, only one cylinder) until the engine is warmed up. It seems to also make the bike more difficult to kick start. Once the bike is warmed up, it tends to sputter at idle, or when decelerating. I have to slightly rev the engine or keep the choke on while it is warming up, and I don't like having the engine run at that high a speed while at idle. I have gone through the points and plugs. All seem to be fine. Additionally, I've worked through "intake leak" test procedures that Cotten linked me to, and found a slight leak between the intake and head, and have fixed that. While my problem seems to have improved a very little bit, I am still having the same symptoms. My guess is that the very slight intake leak I found was not causing the issue, just making it a little worse?

Anyway, I have a relatively new coil on the bike (chinese repop), that I understand are not of the most dependable quality/manufacture, and am wondering if the coil could be causing symptoms like I am having. Again, more difficult to start, missing while idling/warming up after start, and for a while after beginning a ride. Once it's nice and warm, she runs very well.

Would the coil perform differently when the engine is warm ... I'm not sure that would make sense, but am wanting to consider all potential issues.

Thanks.

[Will]

I fought with this for 6 month before I found it. Coil was new. When it was cold it worked fine. When it was running and warm pop and sputtered a bit. When was warm or hot wouldn’t start. Finally borrowed a coil tester that heat the coil up like it had been running for a while and a coil that worked good cold, was marginal. Replaced the coil (with another Taiwan repro) no more problems. According to other people on the site these repro coils don’t like water. You get them wet, you have problems
Good luck
W

[rousseau]

You stated it seems to be only one cylinder. Swap the plug wires in the coil. If the the "good cylinder" is now the one missing ,I'd say you have coil trouble. If not, I'd check the valve (pushrod) adjustment on the "bad" cylinder.

[40 Nuck]

Thanks to you both ... good suggestions ... should've thought about switching the plug wires myself. I may buy one of the Accel coils and see if that makes a difference too. While I don't ride in rain intentionally, the bike has been in wet weather, so maybe that has impacted the coil. While the Accel won't look stock, I can use it until I find a good original, or have one "rebuilt".

Much appreciated.

[40 Nuck]

Update ... I am not getting spark to the rear plug. I've exchanged plugs, and no spark, so I'm assuming that the coil is the problem. It's just strange that once warmed up, the problem seems to go away. As I understand it, usually coils have problems the other way ... work cold OK, but may have issues once warmed up. Anyway, I'm replacing the coil, and will see if that elimiates my problem. Thanks.