Kholer Courage 25HP Vtwin stalls when warm and under load

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lcantu

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
Hi everyone,
I'm trying to diagnose a persistent issue with my Husqvarna 54" riding mower and could use some guidance.

Symptoms:
  • Starts and runs perfectly when cold
  • I can mow for about 15 minutes with no issues
  • After 15 minutes and when under load, the engine begins to surge and eventually stalls
  • If I catch the surge early, I can sometimes prevent stalling by disengaging the deck and lowering the throttle. After idling for ~2 minutes, it will run normally again for a few more minutes before repeating the same symptoms
  • Noticed this mower runs significantly hotter than an identical unit I own—might be unrelated, but worth mentioning

What I’ve Tried (using parts from a known-good identical engine I have):
  • Replaced:
    • Carburetor
    • Airbox w/ filter
    • Fuel filter
    • Fuel pump
  • After exhausting fuel-related suspects, I moved on to:
  • Ignition coils
  • Spark plugs
Despite all these replacements, the issue persists. I'm officially out of ideas and hoping someone might point me toward a less obvious cause for the issue.

Any suggestions on what to check next would be greatly appreciated!
 
Last edited:
ILENGINE

ILENGINE

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
Depending on year of mower there is the possibility of a clogged fuel cap vent. Also there could be debris in the fuel tank that is stopping fuel leaving the tank. After those things check out. I have seen a couple cases were the heat shield that should be covering the exhaust manifolds is bent upward directing the exhaust heat directly on the carb causing the fuel to boil in the carb bowl leading to vapor lock. If it is a fuel boil issue you may hear the fuel in the carb bubbling. And also you won't be able to hold your hand on the fuel bowl due to being extremely hot.
 
A

Auto Doc's

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
I agree with a blocked fuel cap vent, especially if you can mow that long. The excess heat is created because the fuel mixture is getting leaned out and starved from the carburetor. Fuel also cools the cylinder when ideal combustion occurs.
 
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lcantu

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
So, still trying to figure out what to do with this thing
This is what i tried now
  • crank the mower with the fuel hose to the carb not connected and its definetely sending fuel
  • swapped muffler and baffle that sits on top of it with the one i have on the other mower - no change
  • Removed the gas cap and went out mowing without it - no change
  • The thing fires up right away and run mostly ok while not hot and no load on it, the only thing i notice when in this condition is that to make it run the best i have to pull just a tad on the choke
  • Today I completely unsitalled the muffler, removed the gas cap and went out mowing without the hood installed (tought that the hood was somehow restricting airflow or something) - things changed a little bit
    • I was able to mow for 1.5 hours
    • I took my laser thermometer to check if it was getting too hot and, it never happened. I was measuring aroung 200-220 when pointing at the filter - carburetor bowl was lower temp than that
    • It still did the surging thing but as long as i caught it early enough, turn off the deck and let it idle for a bit, it would recover after a while and i could engage the deck again
    • After a while, i noticed that whenever it started surging, i just needed to stop (whith the deck still engaged) and pull the choke and it will recovered
This definetely sounds like not enough fuel is getting to the engine but not sure what else could i do or change....

Other thing i was thinking is timing - do these engine can get out of timing and get adjusted?
Also i was thinking that maybe i can enrichen the fuel mix on purpose - are these carbs adjustable (don't really know anything about carbs, I'm from the fuel injection era :))
 
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Auto Doc's

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
Next suggestion is to remove the top fan/ engine cover and clean the engine cooling fins. Air cooled engines are critical about proper cooling from the flywheel fan. Chaff, dust and debris gather in the fins then cooling is quickly compromised.
 
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VegetiveSteam

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
You may have already checked this but, does the fuel line run anywhere near a high heat source? If so, see if you can re-route it away from that heat. You could be getting vapor lock. Another thing that can help if it is vapor lock is trying some premium fuel. Premium typically doesn't vapor lock as easily. Also, when was the last time it ran with no issues?
 
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Auto Doc's

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  • / Kholer Courage 25HP Vtwin stalls when warm and under load
I think this is leading back to the fuel tank having a partial blockage interrupting the constant fuel flow.
 
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