1. Tap floatchamber with stub end of screwdriver and see what that does.
2. Sometimes draining the floatchamber and refilling is enough
3. Remove floatchamber and check floatvalve for particles. Can be done with carbs in situ. Unfortunately for you it concerns #2 which means you have to do #1 as well.
BTW, I recommend changing the 4 small crossheadscrews for little ss allen bolts that are much easier
4. Whilst you're there it won't harm to unscrew the pilot jet (carefull!)and inpect it for cleanliness. No need to pull the rack.