ZTX5 with ZT740 25hp Kohler with 15 hrs. Full throttle or idle down for stopping engine . I’ve been lowering throttle to idle and I’ve noticed it’s either backfiring of after firing when I shut it off. I’ve been told to shut down at full throttle, mid throttle, and, idle.
On Kohler the recommendation is shutting down at full throttle. The reason on Kohler engines the fuel afterfire solenoid on the carb doesn't shut off the idle circuit of the carb, therefore shutting down at idle allows fuel to be drawn in and unburnt into the muffler where it is ignited.
The alternative it to idle down and then move the throttle to full when you turn the key off. The idea is to get the engine to try to get fuel through the high speed jet in the carb which is blocked by the solenoid.
I think Cub recommends half throttle. Even the Zt740 owners manual states half to full throttle. What happens if the solenoid plunger is snipped off . I’ve heard of this being done. Thanks for the help.
The "stop" mechanism is to ground the coil so no spark
However there is nothing to stop the engine rotating apart from engine compression
So the engine will suck in fuel then blow it out unburned which the EPA will not allow
Thus the afterfire solenoid was introduced which shoves a bung up the main jet so those final 6 or so revolutions there is no unburned fuel being pumped into the atmosphere when you shut off.
As it also prevents the accumulated fuel in the muffler igniting on some of the red hot surfaces it also prevented the after fire .
Marketed as an "anti after fire " device it got public acceptance
If it was marketed as an anti- pollution device then the Republicans would have railed against it .
Cutting it off will cause after fires and of course the unburned fuel pushed out the exhaust will cause life on the planet to cease to exist which may not matter if Tzar Putin I ends up nuking the planet to save face .
