hissing at idle

26mm carbs,i have a hiss or pop sounds like air hiss?is this carb or timing?only at idle,vacuum ports on carbs(2) should they be plugged or put hoses on them.they where plugged when i got the bike,but mechanic said he thinks they should be open?is this the hiss? i do have 15 pilot jet,if that's too small.

2 of them are for fuel bowl vents and one is for "vacuum" to the fuel tap

i dont have the one for the fuel tap.

During normal operation, the two float bowl air vent hoses should exit to open air.
And other nipples should be capped/plugged (usually vacuum nipples on carb holders which are used when syncing carbs).

Good Fortune!

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