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Discussion Starter · #1 ·
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.
 

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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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Discussion Starter · #4 ·
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?
 

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Go ahead and remove the sparkplugs....check the condition...
They may lead you to the problem..
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Discussion Starter · #8 ·
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.
 

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Might be time to check the governor adjustment...
Other possibility is the valves are out of adjustment...
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Discussion Starter · #10 ·
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?
 

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Are your gas caps venting. ?
Fuel valve operating properly ?
When it starts running poorly...remove the fuelline and check the flow..
I wouldn't think it would be electrical...it would show up on the sparkplugs..
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Discussion Starter · #12 ·
Are your gas caps venting. ?
Fuel valve operating properly ?
When it starts running poorly...remove the fuelline and check the flow..
I wouldn't think it would be electrical...it would show up on the sparkplugs..
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Gas caps are venting. I took it out yesterday and with all the bumping around I can see small moist areas near the hole so I think they're ok. I assume the shut-off valve is ok because I've left it closed before by accident and it killed the engine. Opening it allows the engine to start up and run fine. I see the same amount of fuel in the fuel filter all the time...but at some point if if keeps getting worse I'll make a point to check the flow. I did already replace the fuel pump.

Yesterday I tried some Lucas fuel system cleaner and I'll run that through and see how it goes. I'm also running some Star-tron in it and I've used that off and on in the past. I'll see how it goes on the next mow. http://mystarbrite.com/startron/
 

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Discussion Starter · #13 ·
I still have the problem and it seems to be getting worse little by little. Just so you know, the mower has only 170 hours on it, it's stored indoors when not in use and it's only used about 2.5 hours per week at my house.

Here's what I've done so far.
- Checked condition of plugs. They look clean, no black and not fowled. Look great to me. They were new as of this spring anyway.
- Checked flow of fuel by disconnecting the line that goes to the carb and put a hose on the fuel pump on that outlet. Started engine and fuel flows quickly out of the hose.
- Checked fuel filter (blew through it and it looks clean - it was replaced this Spring)
- Checked/cleaned air filters (they were new as of spring too)

I've been using premium gas. I ran a couple cans of fuel system cleaner through the gas too after this problem came about. No help.

Do you think the carburetor is dirty inside? Could that be it? Would it be worth the trouble to take it apart and clean it out (remove the bowl, jets and spray it with carb cleaner). I hate to take it apart if I don't have to though.

The governor seems to work fine. The engine speeds up when under a load like if you take off quickly or start up a hill from a stop...you'll hear the engine kick up in speed.

This couldn't be electrical could it? The way it's acting, it seems more like a fuel issue (carburetor dirty?).

In the past I could engage the blades at half throttle, which is what I think you're supposed to do anyway to be easier on the electric clutch, etc....but now, if I don't have it at full throttle it'll nearly kill the engine when I engage the blades. Even at full throttle, when I engage the blades, the engine slows down and sputters like crazy, running really rough until the blades are up to speed. Then when I start mowing, if I run into some thicker grass and I'm going 3/4 speed or so, it'll start sputtering like crazy again until I slow down so it's not under so much load. Basically, a heavy load is what triggers the problem. Otherwise the engine runs really smooth and sounds great.
 

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M ezmark did the same thing you are describing, and continually got worse until i realized (with help of some fine folks on this site) to look at my coils. Sure enough i was struck with infamous KAW coil failure, the begining stages were just as you are describing.

Good Luck
 

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Discussion Starter · #16 ·
Good news. I decided to take the carb apart and spray it out with carb cleaner. I took the bowl off and also the top plate. I sprayed carb cleaner in every hole I could find. When I put it back together, it still sputtered under heavy load or even a little before heavy load, but after a few minutes it ran strong and plowed throw thick, tall grass in the field (as a test) with no sputtering. It sounds good now. I'll keep an eye on it but I think that's what the problem was. Also, the fuel filter is nearly full of fuel all the time now. Before, it looked nearly empty which I though was unusual.
 

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Discussion Starter · #18 ·
Ok...so knowing what I said in my previous post about cleaning out the carb, what suggestions would you have at this point? Could it potentially be coil related like someone else mentioned? The only thing that makes me skeptical about that is how it only happens under a heavy load when the engine is struggling with tall grass or starting out on a hill with the blades engaged. I would have thought a coil issue would be more consistent and not only happen when it's under a heavy load? Could it still be the carb (maybe I didn't get it cleaned out as well as I thought)?
 

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Discussion Starter · #19 ·
EDIT:
I was just reading some more on here about the coil problems people have had in the past. I'm going to start it up and pull off each plug wire one at a time to see if it runs any differently or dies. It should be an easy way to tell if each plug has spark.
 

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Discussion Starter · #20 ·
I just fired it up and pulled each plug wire off to see how it sounds. For each plug wire, when I pulled it off, there was an obvious change (rough idle and audibly sounded as if one cylinder was now not firing. I did this for each side and it sounds the same when one or the other plug wire is pulled off. So, I think the coils are working fine in this scenario. My question is though, is it possible that they could be failing under a heavy load? Could a coil problem present itself JUST under heavy load?
 
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