Peugeot V-Clic 50 starting & running problem?

The bike is really difficult to start & will only rev if rear brake is applied otherwise it bogs down & stalls? I am NO novice to motorcycles (I build & fix my own custom choppers/bobbers) but this little turd has really got me stumped & I have gone over everything on it at least 3 times! (only thing I haven't done, which is next on my list is new barrel & piston) as it seems to have no compression, yet it will start with persiverance & can be ridden???