[Rai]

The cap on your mower’s gas tank is vented with a small hole. This vent is just large enough to allow air into the tank, creating enough backpressure to aid in fuel delivery to the carburetor. Since the hole is so small, it can plug up with dust or dirt during normal mowing operations. Check and clean the vent. Surging is also caused by water that got into the fuel. A mower left in a heavy rain or condensation on a hot summer day can choke the engine. Empty the gas tank, properly dispose of the old fuel and try a fresh batch of gasoline. here

[leopoldo78fa]

Take a look at the air filter. If it’s dirty, the engine may be starved for air. Filters are either paper or foam. You can remove foam filters and clean them with soapy water, but you’ll have to replace a dirty paper filter. A thin coating of engine oil on foam filters typically helps them attract dirt that could end up in your carburetor. Paper filters, however, only use their pleated medium to catch dirt and dust. An air filter is a quick fix that should be your first stop when troubleshooting a surging lawn mower. here

[nofuture]

When a lawn mower surges, it sounds as if the engine reaches full speed, only to decelerate quickly. Typically, it doesn’t die, but the surging may repeat during the entire time the mower is in use. Like other small engines, mowers rely on a precise volume of gasoline and air for smooth operations. If either of these is exceedingly rich or lean, surging may result.

[fetma]

A dirty or gummed up carburetor causes an engine to surge. If you feel comfortable working on carburetors, unbolt the bowl and clean it thoroughly. Check whether the float moves up and down without sticking, and clean the tiny ports on the bowl hold-down bolt. Some carburetor cleaner applied to the other jets and needle valves help free them dirt. Serious problems -- such as damaged gaskets, broken jets or internal parts that will not come clean -- require the installation of a carburetor kit or a carburetor replacement.

[MagicalTux]

A loose carburetor sucks air in through crevices around the point where it attaches to the engine block. This excess air throws the gasoline mixture out of balance. It also ruins the vacuum necessary to pull gasoline into the carburetor at the prescribed flow rate. Tighten the bolts for a good fit, and check any other bolts that attach the carburetor or the air intake manifold to the engine. [links]

[skull88]

Whether your lawnmower is a shiny new model that's your pride and joy, or an old faithful model that you've had for years, you want it to work correctly when it's time to mow the lawn. A mower with an engine that revs erratically, also known as hunting and surging, indicates that you need to address a problem. Fortunately, this is often a problem you can solve yourself without the aid of a repairman.

[zlavernenasho]

Another problem that can cause revving and dying of a lawnmower engine is a faulty or poorly adjusted spark plug. Check the spark plug to see if the wire is connected to it firmly and not wobbling about. If it is connected correctly, remove the spark plug to see if it's covered with corrosion. If so, a simple scrubbing with a wire brush can restore it to working order. If necessary, replace the spark plug with a new one. Check the spark plug gap with a spark plug gauge to ensure that it's adjusted to the proper setting recommended in your owner's manual. more

[Karmicads]

A lawnmower that hunts and surges may be experiencing something as simple as an airflow issue. If the air that the engine requires to run is blocked, especially sporadically, it can cause the engine to slow down. When the blockage moves or clears, the engine may suddenly rev up in response. To fix this type of problem, check the air filter to ensure that it's not clogged with dirt and debris. Check the vented gas cap as well. Both issues can cause reduced or sporadic air flow, and clearing them will fix the problem.

[oadriannadeleong]

This carburetor style is fitted to a few engines and is prone to gasket failure. The job of replacing is simple and will solve the surging. The process is as follows:

[irstax114]

I would only do this if there is obvious damage to the manifold or I had replaced the carburetor gasket and the engine was still surging. more

[hebrew15]

Spray the cleaner around all carburetor gaskets, anywhere the carburetor meets the engine. The trick is to hear an instant change in engine note, that’s the sign of a vacuum leak.

[William129]

What should I look for to fix it?

[jaymac407]

Stumper, As for having to replace the carb. on your Honda, I've ran across 3 or 4 the last couple years that nothing I did would make them perform properly and never found out why just ended up replacing them.

[gould]

Not trying to be a smart azz or anything I just want to explain how I came to my diagnoses. First, I did inadvertently forget the plug because thats the first thing I check or replace. I eliminated a clogged fuel filter because it requires more fuel to operate higher speeds than lower and the unit in question runs fine on higher speed. Although applying the choke slowly will confirm a problem in the low speed circuit it is not required. If the unit in question had a surge at higher speed then it would require applying the choke slowly to determine if it is a problem in the high speed circuit of the carb. or a governor problem. If the choke is applied and the surge goes away that would indicate a carb. problem, If the surge continues that would indicate a out of adjustment or faulty governor.
While typing this one other detail came to mind, If the engine in question has a small spring on the throttle linkage rod and is broken or disconnected this also could cause a low speed surge. Honda and Kawasaki are critical to having this properly connected. more