Need Help. Toro MX4250 Surging

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Bartman71

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #1

I have a Toro MX4250 that started surging yesterday. I cleaned the air filter, tried Seafoam, checked the fuel filter and added new gas. I looked at the throttle when its surging and can see a mechanical action triggering the throttle. I included a video below showing whats happening.

https://youtu.be/oIY2QRudpcM



Does anyone have any ideas?

Thanks
Bart

 

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bertsmobile1

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #2

Either too much air or too little fule.
So eliminate the first by saturating the manifold with WD 40 or similar from a trigger pack ( NOT A SPRAY CAN ) .
If the mower blows white smoke or significantly changes engine speed there is a manifold leak.

Fairly rare but they do come loose, crack etc.

After that is it remove the carb for a proper clean.

 

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Bartman71

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #3

Thank you for the quick reply.

Whats triggering the throttle to activate? Is the engine trying to adjust to the poor fuel mixture situation?

 

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bertsmobile1

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #4

Bartman71 said:

Thank you for the quick reply.

Whats triggering the throttle to activate? Is the engine trying to adjust to the poor fuel mixture situation?

Click to expand...

Yes.
Governed engines surge because the governor is trying to maintain a speed that the engine can not manage.

 

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Bartman71

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #5

Thank you. I am an IT guy and not very mechanically inclined so am getting a bit worried about fixing this myself.

Do I soak the air filter in WD40 or spray it into the manifold? (I assume the manifold is the area around where the air filter fits on)

 

7394

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #6

Intake manifold: Is the part that the carb bolts to & has runners that bolt to the engine.


You spray around the outside of the intake manifold, where it bolts to the engine, this is where it sucks in when running, so "if" you have a leak it will show out the exhaust as Bert described.

& I would also spray the carb mounting flange.

 

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Rivets

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #7

Bert means saturating the areas between the carb and the engine, that is the intake manifold. If there are no changes in engine speed, that is good, but means the engine is running lean and probably a carb issue.

 

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Bartman71

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• May 24, 2019 / Need Help. Toro MX4250 Surging

• #8

I believe I get it.. So spray WD40 around the manifold to spot a leak... Makes good sense and I'll give it a try in the morning..


Thank you all!
Bart

 

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Bartman71

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• May 26, 2019 / Need Help. Toro MX4250 Surging

• #9

Hello, I took apart the carburetor today and cleaned it using Berryman Carburetor cleaner. I ran a paper clip through the two jets coming up from the fuel bowl and shot the spray through it until it came out the other side. I cleaned the entire carburetor using the cleaner and ran the paper clip through all the holes.

I also sprayed the cleaner around the manifold and saw white smoke. However, i think the spray was landing on the exhaust which was causing the smoke as opposed to the smoke coming from the engine.

The good news was that I was able to get the carburetor back together and the engine started! (I was worried about this . The bad news was that the engine resumed the surging. However, I noticed something today and its that the engine only surges and runs rough when idling without load. Once I engage the blades the engine runs fine.

Looking at the attached diagram I don't think I cleaned the single jet in the bowl (See attached picture)... Could this be causing the surging when idle issue?

 

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bertsmobile1

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• May 26, 2019 / Need Help. Toro MX4250 Surging

• #10

Carbs have 2 fuel circuits.
One for low speed running or idle and anther bigger one for high speed running.
In your case the idle circuit has a blockage in it .
So it is back off with the carb for more cleaning.
And a carb is not a Macintosh so please no paper clips. :laughing:
A strand of copper wire or something softer than the brass the parts are made from.
try this site http://outdoorpowerinfo.com/ and look for the cleaning instructions for your carb.