If it's a motobecane you are working on it's the carb float.
I'd say judging from some of your problems your exhaust pipe may need a good decorbonizing. Of course it's easy to turn over without a plug in it!!! :-)
Come to think of it since you are mentioning the decmpression, I'm thinking you have a motobecane. Correct me if I'm wrong.
Speaking of which, what make/model is the bike?
If it is a motobecane I'll be more than happy to help, as I've learned quite a lot over the past few months from here, and other sources.