KAXS.852N4CA spark plugs are very different looking

[revtim]

Recently purchased a 2010 Toro 74923 Z Master Commercial Zero Turn Mower with 1450 hours on it from a municipality. Cut grass twice so far and it was running but not optimally as every now and then it would start revving faster for 10 or 15 seconds and more like I would expect so I am in the process of changing the plugs, fuel filter and air filter. When I pulled the plugs, the rearward plug was clean and dry but the forward plug is black and a little wet. Both fuel filter and air filter needed changing and the fuel filter might have actually been put in backwards to the flow.
I've always see wet/black plugs as a sign of running rich. The tank was full when I picked it up before and this was before mowing season started in Michigan so I am assuming this gas was from last season.
I haven't started it yet as I will get my air filter today. Seems those things aren't carried locally.
The plugs were very difficult to unscrew... providing resistance all the way out so I am also assuming they have been in there a while.
I've never run across this situation except in an engine with low compression in one cylinder but after just 1400 hours that seems unlikely.

 

[StarTech]

Toro 74923 used a Kawasaki FX751-AS07 engine in all serial numbers.

Never assume anything...I have seen low hour engines to fail.

First do a leak down test to verify cylinder condition. It can be just be just bad valve guide seals as I have seen quite a few times or a blown head gasket. Plus an engine that been overheated could have valve or more that move out of place and crushed the seal.

Even the twin barrel carburetor could have one of the main jets loose as the tiny o-rings do go loose.

And make you are using either 15W50 synthetic or 20w50 dino oil anything lighter does cause problems.

 

[txmowman]

Recently purchased a 2010 Toro 74923 Z Master Commercial Zero Turn Mower with 1450 hours on it from a municipality. Cut grass twice so far and it was running but not optimally as every now and then it would start revving faster for 10 or 15 seconds and more like I would expect so I am in the process of changing the plugs, fuel filter and air filter. When I pulled the plugs, the rearward plug was clean and dry but the forward plug is black and a little wet. Both fuel filter and air filter needed changing and the fuel filter might have actually been put in backwards to the flow.
I've always see wet/black plugs as a sign of running rich. The tank was full when I picked it up before and this was before mowing season started in Michigan so I am assuming this gas was from last season.
I haven't started it yet as I will get my air filter today. Seems those things aren't carried locally.
The plugs were very difficult to unscrew... providing resistance all the way out so I am also assuming they have been in there a while.
I've never run across this situation except in an engine with low compression in one cylinder but after just 1400 hours that seems unlikely.

Use a tachometer to see what rpm the engine is running at high idle. Toro’s spec is 3800 rpm. What do the rpm’s jump to when it increases for 10-15 seconds? If it is above the high idle rpm, it is possible that the engine was overheated and the heat damaged the ball guide if the governor assembly.