Old and new Briggs & Stratton Pulsa Jet carburettor fuel pump diaphragms.
The old diaphragm was off a 30 year old 5 HP Briggs & Stratton L-head engine that refused to start after sitting in storage for several years.
The cause was simply due to the old pump diaphragm stretching and losing the ability to compress the spring and in turn pressurise the fuel. The flapper valve over the inlet port had also stuck closed, which would have prevented fuel from flowing even if the diaphragm had not been stretched.
