are the carbs' choke a lever or a pull to operate? I assume it eventually starts but how? fires on 1 cyl and then 2 chimes in or does it get straight to it? I'd suggest looking at your timing first, that's clean contacts, contacts gap, take off left cover and find LF to check ignition timing. (even better use a strobe) and check RF timing if the bike has had a 400 barrel and head on, the carbs will have had the mains and pilot jets increased so you need to check if they have the correct ones for the 120 and also check the needle position and type. that'll do for starters