Hi and Welcome to the LMF. Those old 5 HP B&S engines are tough but they
do get hard to start over the years. Sometimes the diaphragm gets stiff and it
won't pump gas. Or the pickup tube screen gets dirty; and it has a choke plate
on the carb or a primer bulb. Those bulbs can get cracks in them as well and
have to be replaced. Sometimes I take the bolts out holding the carb to the
engine and remove the carb and diaphragm and see if it is stiff.
I've softened them up by rubbing them back and forth gently together
and it will work for a while. Best to check the diaphragm and replace if
needed. The weak spot on it is the narrowest strip where it often cracks. Poor
design imo. Hope this helps. The spring would be the throttle spring which only
stretches to increase rpm. Spring pulls engine into rpm's, the governor pulls it out.