If the plugs are dry then the amount of fuel for starting is probably not enough........Either use the chokes.......or tickle them a bit more.......Do not use both as this will definitely flood the engine. Once the engine starts, pending if you have chokes of not......You should use one or both chokes to help keep the engine running, or else partially choke one carb with your non throttle hand to keep it running........It is probably just a cold engine, so once its running just use some form of enrichment even if its only on one carb to keep it running enough to warm up.........Sometimes just holding the tickler button down on one bowl will keep plenty of fuel up to that carby.