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View Full Version : 25 HP Kawi - Backfires when shut off


MJfromMD
09-26-2010, 05:12 PM
I have a 2008 Z with the 60" deck. It is sweet and overall I do love it. But since day-1, (I got it new in 4/2008) after use it ALWAYS back fires after shutting it down.

I am certain that there is likely some adjustment that will stop this, but I was wondering if any of you with this engine have (or had) witnessed this same characteristic?

The engine has to have been running to operating temps, (my average cutting time is about 2.5 hours). AFTER cutting, this is the sequence:

When I pull the throttle lever back to idle, but engine speed does not slow down completely like one would think - as other engines do - but instead only decreases slightly. (Sometimes, I pull the choke to decrease the RPM in an effort to avoid the back fire when I turn the key OFF, but it does not help totally).

When I cut the key off and it spins down to stop....its last revolution ends in a back fire.

Note - Before the engine is "warm", (at op temp) the idle speed DOES seem "normal" - in that there is a broader RPM "range" that can be varied with the lever, and no back fire is experienced when the engine is turned OFF.

But when the engine is "hot" its range is much less, and seems limited to remain in the higher RPM range. This probably is the reason for the back fire - since it is keyed OFF while running at the higher RPM.

However, the lever position is setting it at the lowest position. The lever does work correctly, varying the throttle mechanically when observed with the engine stopped or running.

Anyone know this one? :confused:

mike haynes
09-27-2010, 04:58 PM
shut the mower off at 60% or more throttle and it will not backfire.

mowerconsultant
09-27-2010, 05:10 PM
You need to get that throttle adjusted so it will idle.
Shutting it off at lower RPM's will likely help.
I would also check to make sure the fuel solenoid is working.
Whats happening is raw fuel being in the main jet while the engine is shutting down, the vacuum in the engine is drawing it in and then into the exhaust since there is no spark once you shut off the engine, the hot exhaust ignites the fuel and thatís what causes your backfiring.

Pj