bike surge

Having recently changed the spark plugs I managed to have a blast today only to every now and then feel the bike hesitate to slow down when I roll of the throttle for only a second . I've taken the bike apart again ready for tomorrow to have look so wondered if any one else has had similar problems and what the cause might be. I thought the linkages might be sticking but seem fine but will oil them up a bit and give the butterflies a clean . The snorkel is not a good fit either so assuming that always been the case.

Not checked the filter to be honest but the bikes not short on picking up just this hesitation or power still on briefly before the engine braking kicks in . bike was fine before changing the plugs and there's no misfiring either .

Checked bike over connections etc electric and pipe all ok but found both butterflies loose so tightenend up and sprayed linkages etc . Put together and revs way high so seems the loose butterflies had something to do with it , just backed off a the fixed screw to seat the butterflies and all seems well but it's peeing down so won't know til I get out on it