I'd vote for carburetion problem.

1st, understand why "choke" is required--it's required because fuel portion of the fuel/air mixture will "stick" to cold manifold and head passages and not enough make it past intake valve. When manifold and head passages are warmed up, this doesn't happen. The way to combat this is pretty crude, i.e. send more fuel. Note that an actual choke does this by creating more vacuum to draw more fuel through jets. Bing enrichener justs adds more via tube into float bowl, no extra vacuum required (or available).

So, when you shut the enricheners off, the left cylinder goes lean. Think idle jet problems, vacuum leaks, etc. While you're at it, make sure the right side enrichener indeed shuts off.

And yes, it's pretty obvious the intake tract on an Airhead is pretty short and some of it is rubber. Enricheners still needed anyway.

If you've got ignition strong enough to not cause missing under high speed load, it will run the motor at idle, too.