Generator Care Generator Maintenance

10 Reasons a Generator to Bog Down (Quick Fixes)

There is a power outage; you rush to the storage to take out the generator and start the engine, ready to keep your family calm and keep them safe. You start the generator, but it starts to bog down when you plug it in. Disappointments and frustrations start to eat you inside out. The one big question that will occupy your head at a time like this would be, ‘why is my generator bogging down?’

Well! There is a series of possible causes of generator bogging down. It could be caused by:

  • Bad Fuel
  • Wrong Fuel Screw Adjustments
  • Dirty or Bad Spark Plug
  • Plugged Up Main Jet, Pilot Jet or Both
  • High or Low Float Heat
  • Dirty, Clogged Air Filter
  • Faulty Low Oil Sensor
  • Stuck Choke Valve

This post elaborates on these points. It will make you understand the problem better and provide the best way to troubleshoot and fix each problem.

Let’s jump right in!

What Causes a Generator to Bog Down?

What does generator bogging down mean? Bogging down means your generator engine starts, but it doesn’t rev up when you connect the load; instead, it stalls until it stops.

Unlike other small engines, which bog down when you engage the throttle, the generator engine has an automatic throttle that engages itself when the need for more RPM is presented by plugging in a load.

Most of the time, the bogging down is related to the engine receiving less fuel or running lean. If your generator behaves this way or is stalling and dying, this post will help you diagnose the problem and give you the best possible solution.

Here are the top 10 possible reasons why your generator is bagging down:

1) Overloading the Generator

Before you can say your generator is bogging down because it’s faulty, you might want to make sure you’re not overloading the circuit as that would cause the same problem.

Assuming you’ve started the generator, left it to run and hooked up to the inlet box. You get in the house and connect your laptop charger or a simple device charger, and the next thing you hear is the engine bogging down as it stalls.

In such a scenario, there is a possibility you were running the generator at total capacity. When you plugged in the small extra load, the generator overloaded, causing the bogging.

Most of the time, the overload sensor will shut off the engine at once, but it can sometimes bog down as it shuts off.

It’s always best to run the generator at 80% of its capacity to allow the small loads that you might connect light device chargers. The practice also allows the engine not to stay much, thus extending its life.

2) Bad Fuel

Some generator owners have confessed to testing it the generator fuel is ‘good’ by starting the unit to see if it’ll run.

If your generator starts and runs for few minutes doesn’t mean the fuel is in good condition; it could be a sign of ‘bad’ fuel.

If you took the generator out once after sitting in storage for months and never treated the fuel, then the ‘bad’ fuel may cause the bog.

When you leave fuel in the generator untreated, fumes evaporate because of their volatile nature. What’s left is attacked by oxygen, which oxidizes the many additives found in gasoline, turning the fuel into varnish.

And since most types of gasoline are mixed with ethanol, a highly hygroscopic substance, it attracts moisture into the fuel compromising it and reduce quality even further.

The water might be small enough not to fill up the water collection bowl in your generator fuel tank, and the fuel might still have some life in it when you’re starting the generator.

One thing is for sure; this fuel won’t have enough energy when the engine combusts it. That means the engine will try to stabilize at first but bog down when you demand more power from it.

How to troubleshoot ‘bad’ fuel:

Drain the fuel into a clear jar. Check the color of the gasoline. Does it look ‘okay? You can also smell it to check for the normal gasoline smell. If it smells funny or something rotten, the fuel has gone ‘bad’ and must be drained.

I have an entire article on how to drain a generator – check it out. But I will give you a summary:

  • Close the fuel valve
  • Detach the fuel hose from the carburetor and direct it to a fuel drain container
  • Open the fuel valve and drain every drop in the fuel tank
  • Open the carburetor drain bolt or screw at its bottom
  • Drain every drop of the stale fuel in it into the fuel drain container
  • Using a carburetor cleaner, give it a quiet cleaning by spraying the cleaner through all the vents.
  • Close everything up and feed the generator with fresh fuel before starting the engine again.

Does the generator stop bog down? If yes, try swapping your generator fuel with ethanol-free gasoline and use a fuel stabilizer to protect the fuel while in storage and make it viable for 1-2 years.

If the generator still bogs down, then proceed to the next possible cause.

3) Wrong Fuel Screw Adjustments

The fuel screw or the pilot fuel screw is responsible for metering how much fuel enters the carburetor. It adjusts the fuel-air mixture.

When you turn it clockwise or in, it leans the fuel-air mix, and if you turn it counterclockwise or out, it makes the fuel-air mix richer.

If yours is more in, 2-2.5 turns in; the generator will experience idle hesitation or bog. If you plug in the load while the engine is idling, it’ll result in hanging RPMs or slowly drop back to idle RPM.

How to properly adjust the air-fuel mix screw?

The best way to adjust is to wait for the engine to warm up and reach low RPM fully. That can be a challenge when it keeps bogging down.

If your generator starts but bogs down when you plug in the load, consider waiting for the engine to warm up. Else, you’ll have to make an estimation and train-n-error.

Seat the screw slightly and set it to factory settings as the set baseline. With your generator running at low RPM, turn the fuel screw in a clockwise direction until you hear the engine stumble.

Turn the screw in the counter direction until the engine stumbles again while noting the number of turns you’re made.

Now you can adjust between the two settings until you get the highest RPM and smoothest engine run. Next, reset the idle settings and test the generator by connecting the load.

If it’s still bogging down or hesitating, turn the idle screw 1/2 turn and see if it improves. Remove the load for the generator to idle. If the RPM hangs, adjust to richen the fuel-air mix and if it dips below idle, adjust to lean the fuel-air mix.

4) Dirty or Bad Spark Plug

A dirty or a lightly bad spark plug might still start the generator, but when the RPM increases, it might not produce the sparks at that rate causing the generator to bog down.

With the generator off, remove the spark plug boot. Get the proper spark plug removal socket and remove it from the engine. Check for any soot or carbon build-up. If there is, get a soft wire brush to clean the terminals.

Also, check the spark plug gap with a gap gauge or feeler gauge by running it through the gap and check the generator manual for the recommended measurement.

5) Dirty, Clogged Air Filter

An air filter cleans the air getting into the carburetor before it reaches the engine. It’s supposed to collect all the dirt and debris the air might be holding.

With time, this piece is susceptible to accumulating more and more dirt to the point of saturation. It might even get clogged, thus reducing the amount of air passing through.

When that happens, the engine will run rich, receiving more fuel than it’s supposed to with relative to air. That results in reduced efficiency, and the generator could bog down when you demand more power from it.

The best solution here is to take out the air filter, clean or replace it. Use your generator user’s manual to locate the air filter, remove the top cover to access the cartridge or foam, whichever your unit uses.

If it looks like it was soaked in the dirt, replace it. If slightly dirty, clean it using a mild dishwasher soap and running water. Dry it using a towel and fit it back.

6) Dirty Carburetor

A dirty or clogged carburetor can also cause the generator to bag or stall when a load is applied. Mainly this will be caused by plugged-up main jet, pilot jet, or both. It can also happen if the gaskets and seals inside the carburetor are compromised.

The most common cause is a pugged pilot jet because it’s so tiny – the tiniest debris can clog it. You can check for jet blocking and clogging by holding the two jets in front of bright light. You want to see the light passing through them. If not, they are plug.

How do you clear plug main and pilot jet?

Disassemble the carburetor from the generator with the engine off and cool and set it on a towel. Clean the carb exterior with carburetor cleaner and place it on a clean rag.

Using a flathead screwdriver, remove the main and pilot jet (generally found at the center post).

Spray some carburetor cleaner on them and, holding them, spray compressed air through the passageway. You can also use a thin wire strand, small enough to fit through the jet holes or get carburetor jets cleaning tool kit.

While in the carburetor, don’t forget to check the status of the seals and gaskets to make sure they are not worn out.

Also, try spraying some carburetor cleaning into the carburetor vents. If you see the presence of debris or dunk, you’ll have to take it apart for a complete cleanup.

If these parts were clean, there is one thing you want to check before reassembling the carburetor, the float height, which takes us to the next probable cause of generator bogging down.

7) High or Low Float Heat

Assemble the carburetor to the point where you’re left with the float bowl only. Hold the carburetor horizontally with the center post facing you. Bounce the float gently and check its positioning.

It has to be parallel with the float bowl line. If slightly out, the engine is running lean, and if slightly in, the engine is running rich.

How do you adjust carburetor float height?

With the engine running lean being the leading reason a generator bogs down, the float will most likely be more outside.

If that is the case, you’ll need to parallel it by bending the tiny metal tab holding it in place slightly towards the inside.

Check your generator manual for directions on how to adjust the carburetor float height manually.

With that done, you can reassemble the carburetor fully and start the engine to see if it’s still bogging down. If the problem is still there, continue to the next possible cause.

8) Stuck Choke Valve

Another possible reason why your generator is bogging down is a stuck choke valve. If the chock valve, responsible for controlling the amount of air getting into the carburetor, is stuck closed or at the half-chock position, the generator can stall or bog down.

Mostly this happens when the choke’s butterfly valve gets disconnected or when you left fuel in the carburetor, and the varnish builds up, thereby holding the choke valve in the closed position.

At this position, the carburetor will receive restricted airflow. That means the engine will start, but as it warms up and starts calling for more air, it will bog down and stall.

How do you fix a stuck carburetor choke valve?

Start by taking off the air filter and the air filter supporter to access the choke valve. Try moving the choke lever with your eyes on the choke butterfly valve to make sure it’s moving.

At the open position, the valve should be horizontal, opening two entries up and bottom. If closed or isn’t moving, check if the lever is connected. If not, reconnect it.

If the valve is stuck, spray some carburetor cleaner and give it time to soak. Use a cotton swab to force out the varnish in the area while wiggling it gently to free it up.

9) Faulty Low Oil Sensor

A faulty oil sensor is the most common and underrated issue that causes generators to bog down or stall. It could even be that the generator oil level is low, thus triggering the sensor.

The oil sensor can sometimes detect slightly enough oil in the crankcase when the generator starts. However, as the RPM and the operating temperature increase, oil gets dispersed to the engine component.

When you connect the load, the generator rotations increase even more to meet the demand. At that point, the oil level in the crankcase tends to reduce a bit, triggering the oil sensor and causing the bog or engine stall.

Check the oil level and top it up if it’s low. If the engine bogs down again, then consider you have a faulty oil shutdown sensor.

Check on either side of the engine casing. If your generator has an oil sensor, you will see two wires, primarily yellow and white, green, red, or blue, coming out of it.

Disconnect the yellow wire at the quick connect point along with it. Start the generator and see if it’s still bogging down. If it’s not, the oil sensor float is faulty.

Unfortunately, there is no way to replace it. That means you will run the generator with the sensor disconnected. However, it’ll now be your responsibility to ensure the generator has enough oil before you start it.

10) Plugged Exhaust System

Another possible reason a generator would bog is a clogged or blocked exhaust system. After combustion, all the burnt fumes are supposed to leave the engine through the exhaust. If the line is blocked or clogged, these gases will remain in the engine.

It’s a problem that can cause damage in the long run, but it will cause the generator to bog down and probably stall in the short run.

With the generator off and the engine has cooled down, take out the spark plug boot and disassemble the generator exhaust from the engine.

Remove the muffler and brush off any debris and carbon build-up. Next, run an exhaust cleaning brush through the exhaust passage to clear it.

Related Questions

Why is my generator surging?

A generator can surge when you use incorrect or dirty fuel, low fuel level, and low fuel or oil quality. The engine must be fed with clean, fresh fuel that has not been sitting in the storage for more than two weeks untreated. A faulty capacity and AVR could also make your generator surge.

About the author

Sharif Gen

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