pod

Check for air leaks , then if thats ok check for water in the fuel, drain your carb float bowls, the screws are accessed from the RHS , not easy to get at ,you will need a ball ended hex/allen key or a screwdriver, you may need to dismount the fuel pump screws , but leave the hoses on.
Fit temporary drain lines from the wee spout on the float bowls and drain into a jar/ bottle, check for water.
If there is water then drain everything and start with fresh fuel.

Or it may be an electrical thing that clears as it warms like a bad coil plug or lead.Do the RPMs rise and fall with both cylinders or is one pot cutting in and out?
Carb icing doesnt usually happen till you are moving, wont happen at tickover speeds.
Cheers
Pod