Re: WHICH 80cc motor is the BEST
Take the gear cover off the right side of the engine and try greasing the gears. Make sure there's no grease on the clutch pads, as they can slip and squeal if they're coated.
While the cover is off, check the inside of the cover and see if there is a ring of scraped off metal. On some engines, the rods that go through the clutch stick out too far and can scrape on the clutch cover. If this happens, it makes some not too great sounds and can be fixed by adding another gasket or moving the shaft over.