20HP Intek has started surging

I’ll post the model number later if someone needs it, but it’s an 20HP V-twin that has about 55 hours in it. I bought it new in 2021 as a replacement for a used riding mower. It had been perfect until today. It started normally and ran fine for about 30 minutes of mowing when it started surging pretty badly. It’s worse when sitting but still not smooth when under load. At one point right before the lawn was finished it chugged really hard and almost stalled completely, then barely lugged for a couple of seconds and revved back up.

Where should I begin looking for the cause? Other than oil changes and cleaning behind the shroud the only maintenance has been replacing a cracked vacuum tube.

Check the fuel system. Pull the fuel line from the tank to the pump, and make sure it flows freely. Drain into a jar. Let it sit, and check for water. If it flows well, hook that back up, and pull from the carb, and crank the engine, and see how that does. If both of those flow well, I'd look at the carb. Have you cleaned a carb before? From looking at the video, I'd replace the fuel lines for starters.

Hello E.,

The carburetor has a blocked internal air bleed, sediment in the carburetor passages or the fuel line has garbage in it from the fuel tank. Those are the 3 most common things I see on this series engine.

Possibly fuel related. Did you add fuel before this began? Could it be a can of fuel with no top where water, dirt, or insects could contaminate the fuel?

andrewslarge said:

Possibly fuel related. Did you add fuel before the began? Could it be a can of fuel with no top where water, dirt, or insects could contaminate the fuel?

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Yes I did. This mower has a tiny tank so I have to fill it completely to the top or it runs out before I finish the yard.

I guess I’ll be taking the carb apart tomorrow.

I might look for a broken vacuum line going to the fuel pump before tearing the carb apart.

sgkent said:

I might look for a broken vacuum line going to the fuel pump before tearing the carb apart.

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I replaced the vacuum line this spring.

Many years ago I was in the US Army and had a test. The question was “You’re driving down a road in your Jeep and it stops. What’s the first thing you check? C. Gas

Elkins45 said:

an fine for about 30 minutes of mowing when it started surging pretty badly.

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Trash in the fuel tank.

It all starts here....... What type fuel can spout/nozzle do you have? Left, middle or right?

Guessing one had never thought about CLEANING that mower, at all. Cooling fins are probably slimed over. Little Turtle Wax on the deck. Little tire dressing on the tires. Proper air inflation is good too.