Kawasaki FH770D 28HP sputtering under heavy load

I have a previous generation eXmark Lazer Z with the 28HP Kawasaki FH770D KAI. Over the last month (I only use it about 1 per week) I've noticed that under a heavy load, such as stopping on a hill with the blades engaged and then starting to go up the hill again, the engine will sputter a little. It seems to be getting a little worse now and to me it sort of sounds like it's starving for fuel. It runs great otherwise and only has less than 100 hours on it. I put a new fuel filter on early this year as part of normal maintenance. So when I looked down at the fuel filter to see how much gas was in it while the engine was running full speed with the blades engaged, I was surprised to see only a small puddle of fuel at the bottom of the filter. I would have thought it would be mostly full. The question is, how full should that fuel filter be when you look at it with the engine running full speed? Maybe the fuel pump is going bad? Though it has less than 100 hours on it, this mower was a leftover and sat unsold for close to 3 years before I bought it. Not sure if that has any affect on the fuel pump condition. My idea was to go the easy route and replace the fuel pump to see if that's the problem. Make sense? Is it abnormal for that fuel filter to only have a small pool of fuel at the bottom??? I would have thought it should be at least half full or more if the pump was working well.

 

Anyone? Fuel pump?

 

Fuel filters are hard to read...sometimes they look empty and work just fine..
Changing the fuel filter...as well as the sparkplugs ...would be good to do to a 3 year old machine...
The crap they are selling us for fuel causes its own problems....
Try a fuel additive and a better grade of fuel...
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I replaced the filter this spring and if I recall correctly I put new plugs in too. I went ahead and replaced the fuel pump today and I thought it was fixed. The first 5 minutes or so was great but then it started doing it again. I took it into some thick grass and it sputtered like crazy. As soon as I was out of the thick grass it ran perfectly. It was overgrown grass I used for testing this problem. I used high octane (93) fuel all the time.

Could it be related to the governor?

 

A good carb cleaning would be a good and en-expensive way.

 

Thanks. I was thinking of trying that next. Maybe just run a high quality carb/fuel system cleaner in the gas on the next run.

 

Go ahead and remove the sparkplugs....check the condition...
They may lead you to the problem..
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I checked the plugs today. They look great. Very clean. I confirmed that I did change the plugs with new NGK plugs this spring. I found the old boxes I kept to get the right part number again next time.

 

Might be time to check the governor adjustment...
Other possibility is the valves are out of adjustment...
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Update: I took it out again after it cooled off (and after having checked the plugs). I do believe heat may have something to do with it. Maybe? Like the last time I took it out today (after replacing the fuel pump), it runs very strong even under very heavy loads in really tall grass. After about 5 minutes though, it starts the sputtering and cutting out again. If you get into lighter conditions (not tall grass and not starting out on a hill), it runs very smooth and no sputtering. It always runs extremely smooth until it warms up for about 5 minutes of mowing and then it starts sputtering again when you get into a heavy load situation (like heavy grass, turning around on a hill and then going forward up the hill, etc).

Does the warming up 5 minutes and then it happening again scenario tell you anything?