Two stroke engines, usually what you’ll find in something small like that rev a lot higher, burning fuel that much faster. Two stroke motors are also almost always going to be carbureted, which effects fuel economy and emissions to a degree too. Cars use 4 stroke motors, that are usually monitoring fuel with various (and if you work on cars, they seem to be endless and everywhere!) sensors and tuned fuel injection systems that are fairly precise. The big kicker though, is the catalytic converter. The catalytic converter is past the exhaust manifold way before the muffler in most cases. This turns a lot of the junk and such in the cars emissions into something less harmful. All cars release a little bit of junk in the air, but newer cars are much better at it than oil burning 3 mpg 70’s carbureted dump trucks in the past for sure. The biggest reason is, most people are gonna have a car in their lifetime here in the US. Or, it’s at least part of their daily lives in the form of a bus or taxi. Garden tools, not so much. Our focus on emissions is mostly on the transportation and power generation sectors in my experience and observation, so things like EFI, efficient cylinder heads, exhaust system airflow, ignition systems, catalytic converters, even the design of the body and transmission that effects pollution are implemented into our cars today. Your dad’s backpack leaf blower on the other hand, is a different story. People want to put gas and oil in it and have it run until it eventually spins a bearing without spark issues, sensor issues, and most obviously, a 15 pound catalytic converter. People want fuel efficient and environment friendly cars more than they do efficient leaf blowers and lawnmowers, so engineers have to make do.
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