Small Engines (Lawn Mowers, etc.): Kawasaki FH541V AP5363 Backfiring, kawasaki model, floor burnisher

Question
Engine: Kawasaki
Model: FH541V
Serial #: A95363
Code: S-06
HP: 17.0
Hours: 1178.4
Fuel: LP Gas
Oil: SAE 30W
Use: 27" High Speed Floor Burnisher (Buffer)

Machine starts and runs @ 3200RPM without load.
Machine runs @ 2900-3100RPM with load applied.
Will run well and without any signs of a problem until it is idled down and then brought back up to speed. When the throttle is opened the engine backfires slightly before going back up to full speed.

When it backfires it blows the tube off the back of the carb filter case that leads to the side of the valve/cylinder.

Any help here is greatly appreciated.

Many Thanks,

David

Answer
David
There are several ways a backfire can be caused. Actually, raw fuel is getting into the exhaust manifold and igniting from hot surfaces, residual combustion, poorly timed ignition spark, burned valves, or excessive heat build up such that raw fuel or fumes can be ignited. Sometimes a backfire will cause an engine to run backwards for a few revolutions.

My best guess is that the exhaust vavle is opening too soon during the power stroke in other words when the gasses ignite. which goes back to timing i assume? it seems obvious because when an engine is running normally, the cylinder absorbs the ignition explosion and realeases the exhaust at a stable pressure.

Valve timing, ignition timing, burned valve, sticking valve, too much un-burned fuel collecting in the exhaust. Any of these timing is off so you get raw gas in you exhaust heat from you exhaust ignites the fuel and bang a nice loud back fire.