Engine Scag engine sputters after a few minutes of cutting grass

Billconwell

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  • / Scag engine sputters after a few minutes of cutting grass
...have a Scag Saber tooth Tiger STT - 31BSG w/ Briggs Daihatsu Vanguard 31hp model DM950G engine w/ 997 hrs. Just recently replaced idler pulley on the 72" cutter deck along with the idler tension spring. Engine starts and runs just fine, once you engage the PTO everything seems fine, after mowing approx 10 minutes the engine starts to sputter, when I quickly disengage the PTO the engine recovers and runs fine again. I checked the cutting deck and all the spindles and pulleys seem to be rotating as advertised. Pulled the plugs they all look identical, fuel pump seems to be putting out normally. I did notice the blade cutting belt seemed unusually hard to reinstall when I replaced the deck idler pulley. The spring looked like the original, which broke during my last cutting (that's when I discovered the bearings in the deck idler pulley were bad). Is it possible I have too much tension on the decks blade belt? ...Any ideas would be appreciated!
 

55TBird

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  • / Scag engine sputters after a few minutes of cutting grass
Have you checked your fuel filter? Sputtering then recovering sounds like fuel is not getting through continually. Fine contaminants caught in the fuel filter can interrupt fuel flow then move around to change the amount of blockage.
 

mrmachinist

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  • / Scag engine sputters after a few minutes of cutting grass
...have a Scag Saber tooth Tiger STT - 31BSG w/ Briggs Daihatsu Vanguard 31hp model DM950G engine w/ 997 hrs. Just recently replaced idler pulley on the 72" cutter deck along with the idler tension spring. Engine starts and runs just fine, once you engage the PTO everything seems fine, after mowing approx 10 minutes the engine starts to sputter, when I quickly disengage the PTO the engine recovers and runs fine again. I checked the cutting deck and all the spindles and pulleys seem to be rotating as advertised. Pulled the plugs they all look identical, fuel pump seems to be putting out normally. I did notice the blade cutting belt seemed unusually hard to reinstall when I replaced the deck idler pulley. The spring looked like the original, which broke during my last cutting (that's when I discovered the bearings in the deck idler pulley were bad). Is it possible I have too much tension on the decks blade belt? ...Any ideas would be appreciated!

I had a similar issue on my tiger cub. Check your PTO clutch and make sure it has not shorted out. It was pulling more power than the charging system could put out and then in turn would kill the battery.
 

javiebrock

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  • / Scag engine sputters after a few minutes of cutting grass
I had a similar issue on my tiger cub. Check your PTO clutch and make sure it has not shorted out. It was pulling more power than the charging system could put out and then in turn would kill the battery.

How do you check your PTO clutch? My STT - Kawa 61" suddenly started to lose power to the blades while mowing. When I shut the blades off the engine runs fine. When I engage the blades they spin, but the power is anemic and even the slightest grass will bog it down.
 

mcdonell

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  • / Scag engine sputters after a few minutes of cutting grass
Sounds like a lean fuel condition that develops after the mower is in use. You can test this theory by applying some choke as the engine starts messing up. If the choke helps, then your running too lean.

How clean is your gas tank? As the engine runs trash can gather at the fuel tank outlet, in the fuel line, and/or in the carb bowl.

I have had engines on tractors and generators do the same thing. I usually just disconnect the fuel filter and check the fuel flow. Sometimes I just blow up compressed air up into the fuel line back into the tank, with the gas cap off.

Water present in the fuel can do the same thing. Engine starts and begins draining water from the bottom of the fuel tank and/or carb. There are many products to help burn watered fuel. My favorite is Berrymans B12. I have this problem with my diesel truck every once and awhile on a 110 gallon tank as it nears the bottom.

Hope this info helps you. Good luck.
 

javiebrock

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  • / Scag engine sputters after a few minutes of cutting grass
I figured it out finally. After removing switches, tracing wires, etc... it turned out to be a plug wire had jumped off the plug. Man, did I do the happy dance as it is rare not to have to spend significant bucks to fix something on this machine.
 

mcdonell

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  • / Scag engine sputters after a few minutes of cutting grass
I figured it out finally. After removing switches, tracing wires, etc... it turned out to be a plug wire had jumped off the plug. Man, did I do the happy dance as it is rare not to have to spend significant bucks to fix something on this machine.

Glad you got it figured out.
 

Billconwell

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  • / Scag engine sputters after a few minutes of cutting grass
...have a Scag Saber tooth Tiger STT - 31BSG w/ Briggs Daihatsu Vanguard 31hp model DM950G engine w/ 997 hrs. Just recently replaced idler pulley on the 72" cutter deck along with the idler tension spring. Engine starts and runs just fine, once you engage the PTO everything seems fine, after mowing approx 10 minutes the engine starts to sputter, when I quickly disengage the PTO the engine recovers and runs fine again. I checked the cutting deck and all the spindles and pulleys seem to be rotating as advertised. Pulled the plugs they all look identical, fuel pump seems to be putting out normally. I did notice the blade cutting belt seemed unusually hard to reinstall when I replaced the deck idler pulley. The spring looked like the original, which broke during my last cutting (that's when I discovered the bearings in the deck idler pulley were bad). Is it possible I have too much tension on the decks blade belt? ...Any ideas would be appreciated!
Follow up:
...Thanks for the great input, I changed the fuel filter and during that process I noticed that one of the coils appeared to have a loose connection. After crimping the blade connection she started right up and ran/performed as advertised. Am assuming she ran on 2 cylinders until the load became too great and would recover when load (PTO) was removed. Again thanks for the input!!
 

mrmachinist

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  • / Scag engine sputters after a few minutes of cutting grass
How do you check your PTO clutch? My STT - Kawa 61" suddenly started to lose power to the blades while mowing. When I shut the blades off the engine runs fine. When I engage the blades they spin, but the power is anemic and even the slightest grass will bog it down.

It looks like you found your problem but I figured I'd still answer your question.

If you unplug your pto clutch and use a multi-meter set to real ohms, the resistance between the terminals should be .01-.1 (I read that somewhere not 100% on those numbers). If it shows 0 or OL or short depending on your meter, the clutch is bad and will pull too many amps and can cause all kinds of issues, burned switches, wires, kill your charging system, etc.
 
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