This is a commercially used 346XP that I built several years ago. It's seen a lot of heavy use. The customer stated that it idled high an a new carb didn't help. When I got the saw I fired it up and played with the tune. It idled a little high, but not too bad. More significantly, the low side wouldn't tune and run quite right. I pulled the muffler and checked the piston. It looked great. I pulled the carb and found the impulse line had a significant hole in it. I thought I had found the problem. I replace the line and it didn't run/tune any better. So, I set the saw up for a vac/pressure test. I simply put the hose in my mouth and blew and could hear a significant air leak. It takes a BAD leak to be able to hear it that easily. I immediately knew I had a bad PTO side crank seal leaking. Thankfully, the user knew not to continue using the saw and took it out of service before any damage was done. Below is a video showing you what it looked like.