Kohler Command 25 Back Firing when letting off the engine as blade exits log

[Drafthorse]

I have a Woodmizer LT40 HD. Recently the motor started back firing as you let off the power coming out of the log. It only back fires once then settles into an idle.

[MartyParsons]

What is the base idle setting? RPM. 

1800 RPM Low setting
3750 for High setting. Governed RPM

Lean condition could also cause back fire. Intake system sucking air. Muffler leak is also something to check. 
Hope this helps. 
Marty

[esteadle]

Backfires are caused by unburned fuel and hydrocarbons getting out of the combustion chambers and into the exhaust system where they ignite and explode. Incomplete combustion comes from weak spark, leaky valves (especially exhaust valves), rich mixtures, and insufficient air. 

The Kohler troubleshooter also suggests: 
 Bad fuel
 Dirt in fuel lines
 Overloaded engine 
 Dirty air cleaner
 Faulty spark plug

See here: 
Troubleshooting | KOHLER

How many hours on this engine?
When was the last time you did a full maintenance (oil, oil filter, plugs, fuel filter, and air filter)? 
I just did mine for the year and I swear my CH730 is running almost better than new.

[esteadle]

> It only back fires once then settles into an idle.

I think maybe the air filter needs changed. If it was something else, it might keep backfiring. But right after the governor cuts back on the fuel feed at the end of the cut, it's just a bit of extra fuel getting past the exhaust valves, and if not enough air, i could totally see this happening. 

[47sawdust]

I've had that happen to me and after cleaning the air filter it stopped.

[ladylake]

 
 Also if it has a muffler screen make sure its not clogged.   Steve

[Ben Cut-wright]

I have a Woodmizer LT40 HD. Recently the motor started back firing as you let off the power coming out of the log. It only back fires once then settles into an idle.

Backfiring out the exhaust or intake?  Severe loud bang backfire or light pop?  Have you pulled spark plugs to check their condition?  Fouled plugs, and even slight amounts of oil in combustion, can cause backfires.  Compression and leak down tests can point to, or possibly eliminate,  head gasket and valve problems, both likely causes of backfires on these engines.

[POSTON WIDEHEAD]

This is how my ex-Kohler started.
It would saw like a new one going through a log but when the blade came out of the cut,
the (TPS) Throttle Position Sensor was giving the engine to much gas and not backing off.

[Oliver05262]

I'd look for an exhaust leak. When the engine idles back quickly, air can be pulled in and the excess oxygen lets the rich mixture ignite in the muffler.
(DISCLAIMER) this is based on my experience years ago with White and I-H gas mixers and log trucks. You could let off the throttle in traffic, count one-two, and scare the life out of someone on the sidewalk!! Not nice to do, so I was careful. most of the time............