Welcome to BHQ !! Start by cleaning carbs one at a time , completely disassemble write down sizes, set float height inspect float needle valve. Sync carbs install choke crossover tube. Do comp test, WOT fuel off kick till gauge stops , threads same as plug. Do all diagnosis BEFORE tearing apart. Granted a weak engine will be hard to start BUT just because it's hard to start doesn't mean it needs to be rebuilt. Tired of everyone just saying rebuild , then you'll be back saying my freshly rebuilt engine is hard to start. JMO , your results may vary.