I would check the air filter and fuel delivery first - clean out fuel tank, check tank breather, change fuel filter etc.
But yes next as per your mechanic, I would try cleaning out the carburetor with carb cleaner and carefully reassembling with a carb kit.
If that didn't cure it I would move on to a leak test. To do this you need to remove as much casing as possible, starter rope, handle and muffler. Now you need to seal both ends of the crankcase. Generally I put the carb back on with an extra piece of rubber to block the intake area and use the muffler bolts and bits of wood to press another piece of rubber on the exhaust port. Then I pump air into the spark plug hole using a bung into an adapted/butchered spark plug. Pump up to 7 psi and look for leaks, rotate the crank. However leaks are often hard to find so I often resort to dunking the whole saw in water and looking for bubbles.
Let us know what you find.