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FH531V runs rough under load after 10 min

Discussion in 'Mechanic and Repair' started by byronlong, Jul 19, 2013.

  1. byronlong

    byronlong LawnSite Member
    Posts: 14

    I have a Husqvarna ZTR with a Kawasaki FH531V AS05. Crank it cold and it runs great for the first 10 minutes. After that, it starts sputtering when I put it under a load by thrusting forward quickly on the handles.

    The warmer it gets, the more it sputters when moving forward till I'm just crawling while trying to cut grass. If I stop the forward motion but leave the PTO engaged, it will catch back up and run okay. It is only under a load that it acts up. Doesn't take much of a load the warmer it gets. It never totally dies out.

    I first started noticing this about a month ago when I would engage the blades. It would act like it was going to choke down but then catch back up and be fine. Now it does it all the time once the mower is hot.

    I installed new plugs and fuel filter. Cleaned out the air filter. Fuel is only a week old. I also checked the kill switch under the seat to make sure the connection was clean and making good contact.

    I called a repair shop and described the issue. They said to replace the fuel lines as they could be softened and collapsing and cutting off flow. The fuel lines appear to be firm and it gets plenty of fuel before it gets hot.

    Another shop said to run some sea foam through it that the carburetor could be dirty. If that was the case, I'd expect it to act up even before it warms up.

    I'm leaning toward a bad ignition coil myself. I took the two coils off and cleaned them with sand paper and a wire brush. Cleaned the magnet good on the flywheel as well and re-installed and set the gap. No change in the performance of the mower.

    Anyone else experience this sort of issue?
  2. BigFish

    BigFish LawnSite Gold Member
    Posts: 3,254

    Well, what did the plugs look like when ya pulled them???
    Did ya check the fuel pump output when hot?
    Could be the inline fuel check valves.
    Did ya pull the fuel solenoid off and check the unit and bowl for crud, etc.?
    Have you adjusted the valves lately?
    Could be a coil, but i'm thinkin' fuel issues.
  3. byronlong

    byronlong LawnSite Member
    Posts: 14

    Runs good under a load at full throttle before it heats up so I dismissed issues with fuel line or check valves. I'll check the fuel solenoid for trash and the fuel pump output next time I heat it up. I have not had the valves adjusted. How often should that be done? This mower has 378 hours on it.
  4. herler

    herler LawnSite Fanatic
    Posts: 5,144

    I'm pretty sure it's one or the other coil.

    It is a V engine meaning you have two cylinders.
    One or the other of the ignition coils is going bad.
    When it heats up you're losing spark on one side, that causes it to sputter.
    The hotter it gets, the worse the problem.

    Finding out which coil is doing it would be one option.
    Simply wait for it to warm up and start sputtering.
    Shut it off, disconnect one spark plug wire...
    Try to start it, if it runs at all it's likely the other side.
    And if it won't even start, chances are it's that side.

    Turn it off again, and to confirm your suspicions reconnect the one side and disconnect the other.
    Repeat the above test.

    You should, by now, have a clear idea which side coil you need to replace.
  5. Snyder's Lawn Inc

    Snyder's Lawn Inc LawnSite Platinum Member
    Posts: 4,541

    Fuel lines might feel ok on the out side but the inside might be stopping fuel I had a line look and felt ok but inside the line had collapse

    Like Herler said it could be a coil
  6. LandFakers

    LandFakers LawnSite Fanatic
    from CT
    Posts: 6,229

    Same thing was happening on my Lazer. To the point where it stopped running on a property. Dragged it on the trailer and drove home and it started right up. Had to replace both coils and that solved the issue
  7. retrodog

    retrodog LawnSite Silver Member
    Posts: 2,421

    Its just one coil if it stays running, we check while running, but you could get bit doing it...lol. pull plug wire while running, we also have a fire tester to see how much fire that side is producing, but easy way to do without tool is while mower is off hold wire away and turn the key over short term you can see spark jumping if one side is weaker jump theres your culprit. It could be fuel related too, maybe lines, carb, bad fuel pump, take hose off fuel pump turn key if its good steady stream you are prolly good on lines and pump...
  8. byronlong

    byronlong LawnSite Member
    Posts: 14

    Thanks for all the suggestions and comments so far!

    The old plugs both looked the same when I pulled them but I replaced them anyway. No change in performance.

    I admit that I have ran some fuel with ethanol in it but 90% of the time I make special trips to a station with non-ethanol fuel for all my small engines.

    I pulled the fuel line off the carb and turned the motor over. Fuel flow was good. Took the fuel solenoid off and checked the bowl. Clear as a bell.

    I'd like to be able to check the fire when running but it doesn't act up when just sitting there at full throttle even with the blades engaged. It's when you start the forward motion that it starts sputtering and I have to go very slow through the grass. I thought maybe it's a problem with the ignition switch. Maybe a short when moving but I don't experience it until it heats up so I dismissed that idea. Should do it all the time if that was the case.

    I've come across several cases on-line of coils going bad on these engines with the same symptoms as mine. I found a coil on Amazon for $55. I'm going to order two and replace them both one at a time to see if I can identify which one is the culprit. I'll keep the old one that is still functioning as a spare.

    I'll update the post as soon as I know the outcome of replacing the coils.
  9. Valk

    Valk LawnSite Silver Member
    Posts: 2,711

    Had a KAW coil issue with essentially the same symptoms...though I could detect a raw fuel smell in the exhaust from the non-firing cylinder. It was so intermittent that it drove me bonkers.
  10. sjessen

    sjessen LawnSite Gold Member
    Male, from Knoxville, Tn
    Posts: 3,329

    With the engine running pull off one plug wire at a time. If the engine dies you've found the bad coil. If not, its the other one. Best advice is to replace both at the same time and keep the good one as a spare.

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