A friend gave me a Sears self-propelled 6.0 HP lawn mower because he got
tired of messing with it. It's not very old and the symptoms are:
When it's cold, it takes 3 or 4 pulls to start it. After it starts, it
runs fine even until the tank runs out. If you turn it off after it runs
for just a few minutes or much longer, then it will not start until the next
day. I have another Sears that isn't self propelled, but the carbs were
identical. I swapped carbs between the two and the symptoms are the same,
that is, the trouble stayed with the self-propelled.