Start problems

I have an schwinn occ stingray chopper with an 48cc starfire chrome.
Pull start centrifugal clutch. Starts fine with pedals 15 to 20 feet, but won't pull start. Exhaust is home made. Muffler is same size as original but 14" long. Exhaust pipe is same size but is 20" long. Pipe inside muffler is 1/2" with 12 1/8" holes in each section just like stock. Packed with a little steel wool.
50th rear sprocket (hills) and i weigh 200lbs 5 ft 11''
any help would be appreciated.
Thanks

mybike

Thanks tommydrakas, i've sprayed the engine and don't sem to have leak anywhere. As soon as i get a chance i'm going to play with ignition. 6" of snow and 9* out right now pluss 15mph winds. No heat in my garage.

Mybvike