Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Why does it backfire when shut off hot?  Have noticed that if it idles 15-30 secs before turning off it does not backfire. What's causes the backfire?

The problem is that when you shut it off without letting it idle for  a bit, as the pistons wind down, they draw a little gas/air mixture into the cylinder.  Since there is no ignition, it is expelled throught the exhaust valve into the hot muffler where it ignites, causing the backfire.  Letting it idle a bit gives the muffler a chance to cool down.  Some Kohlers have a fuel shut-off solenoid that prevents this from happening.

My 25HP Kohler backfires often.  I should look into the solenoid and see if it can be retrofit.

LL

the more economical engines will usually do the backfire deal.

i say engine but in reality it is the tractor manufacturer that adds the muffler most times.

the same tractor can have many different engine options.

for example the huskies we sell come with kohlers and kawies.the kohler will always backfire and the kawies never do .same mufler with each engine and the kohler on these tractors has the solinoid on the carb and it still backfires.

its just the design...usually a large single cylinder engine .

you should run it at half throttle for 30 seconds or so and then shut it off.

later chris 

Or just don't chop the throttle off when shutting it down, especially if it has an emission carburetor.