Joaquin,

When the engine is at idle, it is not quite pressurizing the tank. I would up the throttle a little for a few seconds to get the tank pressurized properly. Anyway, you should idle reliably at 2000.

Also check that your regulator screw is flush with the housing. Other than this, I do not know what to suggest except to ask Dave Shadel himself in the YS Engine support forum.

Azhar