My neighbor had a 20 year old Stihl chainsaw that was getting harder and harder to start. If the saw had been running for 10 minutes or so and then shut off to refuel, it was impossible to start until it had cooled off. We rebuilt his carb, installed a new plug, and he always burned fresh gas. Still no luck! I looked at the coil and noticed the gap between the contacts and flywheel looked excessive. The coil was not testing well, so I put a new coil in and gapped it correctly. The saw now starts like new and restarts with one pull once warmed up.