Wow, whistling?! I guess LC motors aren’t as sensitive to minor air leaks. Most bikes have a carb for each cylinder and control air/fuel mixtures for engines that are 1/10 to 1/20 the size of the 2F tractor engine. When I'm working on a bike that's running like crap I get excited when I find a vacuum leak, it's usually a pretty easy fix. Looks like it is a machined fit, none of the carb diagrams showed anything resembling a seal.