You made my point rather then leaving the throttle control where by the engine speed is reduced and then it shuts off using-up all the fuel vs spewing raw fuel in the environment when shut off at high speed. How did the EPA approve this mess.
You need to have a little think about what you are saying and get things into perspective
1) on a single speed engine there is usually only 1 jet, the main jet and the fuel solenoid rams a stop into it, thus there is no fuel available to the venturi to be sucked into the carb, so no unburned fuel coming out.
2) On a carb with an idle jet, the idle jet is generally richer so idleing down runs a richer mix than the engine can burn completely thus pumping out some unburned fuel before you shut down.
3) it is a small engine 320 cc which does about 50 power strokes on shut down till stationary.
4) most engines are wired so the alternator goes dead short to increase the load on the engine to shut it down faster and may more have a flywheel brake to again shorten down the rundown time.
5) the volume of the carb float bowl is around 50cc and if you shut off the fuel, that 50 cc will run the engine for around 3 to 5 minutes, the engine stops after shut down in less than 30 seconds = around 8 cc of fuel.
Opening a can of fuel that has been sitting in the hot sun for an hour will release more unburned fuel than that into the atmosphere.
6) Thus we are talking trash in the overall picture of things, unburned fuel after shut off would equal about 0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 % of global pollution and would be about equivalent to the amount a person farts each day.
The pollution generated by the people researching this, writing legislation running the air conditioning in parliament house while the bill is debated, making all of the paper to amend the act, pulping all the old obsolete acts then distributing the new legislation would be in the order of 1000 x the pollution the act seeks to prevent occurring.
It is TRASH LEGISLATION designed to make it look like some one is doing something while all the time doing nothing.
One obsolete 747 taking off fully loaded at an airport where they can not use afterburners will pump out more unburned fuel than every mower in the entire continential America running for an entire year, and there are around 200,000 obsolete 747's flying in the USA alone doing around 10 take offs a day.
Now just so you see where my mind is at, I have nothing about pollution legislation that has a real outcome, reducing car engine sizes, enforcing minimum MPG figures for motor vehicles, enforcing home insulation laws. These things make sense and will have a net outcome. Shutdown solenoids will not.
There was even a move to replace all 2 strokes with 100% ethanol burning engines mixed with vegetable oils , that makes good sense, and I supported it, putting ethanol in regular fuel does nothing other than make profits for the ethanol companies shareholders.