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Did you ever try backing out your mixture screws about a 1/4 turn (possibly a 1/2)?
When you remove the snorkel, you should have to back the screw out a bit, but shouldn't have to re-jet.
This would give you a tad more air in the idle circuit. You may just be a hair rich and unburnt fuel is slipping into the header and buring there. The tad of air may help it combust in the cylinder.