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.

 

[Auto Doc's]

Hello revtim,

Sounds like one cylinder not producing power.

A quick check is with a spray bottle to see if water burns off of each exhaust outlet rapidly. If one does not, you found the none working cylinder.

Simple is the best approach: Start by replacing the plugs.

Next would be a possible coil failure. There are many You tube videos that can help replacing one a setting the proper air gap.

If the upper engine cover has never been off for a good cleaning, overheating of the cylinders and a failed head gasket are a real possibility.

Here is a parts source according to your engine number

PartsTree - Home of OEM Parts for Outdoor Power Equipment

Parts lookup and repair parts diagrams for outdoor equipment like Toro mowers, Cub Cadet tractors, Husqvarna chainsaws, Echo trimmers, Briggs engines, etc.

www.partstree.com

Keep us posted on what you find, because many of us can easily write a lot about "what it could be" but let's take it a step at a time with the diagnostics first.

 

[revtim]

Thanks for all the input... I should mention that the pan beneath the engine has oil on it...evidence of a leak but don't know from where...
Also, Do the valves on this engine need to be adjusted?

 

[Auto Doc's]

Hi revtim,

You might check on Ebay and see about getting a manual, CD or download copy, so you have more information to work with. Having the actual repair and service data is far better than some of the wild guess fixes that show up here at times.

I buy most of my small engine and equipment data through Ebay.

 

[Auto Doc's]

Here is a video by Teryl Fixes All, go to the 5:40 time to skip the BS humor skit, he loves to do them:

Kawasaki FX751-AS07 engine - Search Videos

www.bing.com

 

[Tiger Small Engine]

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.

How can spec be 3800 RPM when maximum for a small engine is 3600 RPM?

 

[Hammermechanicman]

Thanks for all the input... I should mention that the pan beneath the engine has oil on it...evidence of a leak but don't know from where...
Also, Do the valves on this engine need to be adjusted?

All kawasaki engines at around 800 hours needs the govenor shaft seal replaced. There are vids on the tube.

 

[Auto Doc's]

If it is exceeding 3600 RPM, the governor has been played with in the past or it is failing and sticking. It needs the governor shaft checked for binding or wearing into the engine case and or a correct governor adjustment.

It been years since I have seen a governor shaft binding or badly worn, but it is possible.

Coming from a municipality, anything is possible because most barely service the engines and run them to death. 1450 hrs. of commercial use are high hours in this case.

If lucky, just a new governor shaft seal and proper adjustment will keep this running quite a while longer.

Loosing oil is never a good thing.