1967 250s starting problem

It should have two Solex progressive two barrel carbs. The floats in these carbs. tend to go bad with age. They'll slowly sink, raisinig the fuel level in the float bowl(s). The floats (on mine anyway) are the same as the VW bug single throat carb. Years ago the dealer wanted $45 for one. I got two used ones for $5 at the local VW parts specialist. I would check the choke settings first though. Does it start? Does it load up (chug, chug) with lots of black smoke when running? When's the last time you cleaned the "oil bath" air filter? Let us know what you find.