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ATV Flooded With Gas – Here’s why and the fix

A constantly flooded ATV is a real pain in the ass, not to mention it’s bad for engine health. Flooding causes gas to dilute the engine oil, and that, over the long term, can be terminal. Anyhow you are in the right place, I’m a mechanic, and I think we can get this puzzled out right now.

ATV gas flooding is a symptom closely associated with the following common ATV issues:

  • Clogged air filter
  • Spark plug fault
  • Soft battery
  • Bad gas
  • Coil fault
  • Carburetor fault

In this post, you’ll learn why your ATV floods with gas, you’ll learn how to diagnose the root cause, and how to un-flood your bike quickly. In addition, you’ll learn some mechanics tips for avoiding flooding in the future.

ATV parked in field

Symptoms of ATV Gas Flooding

I think you have this one covered. The symptoms are obvious to most, but there may be a few in the list below that are tangential to flooding.

  • No start
  • Long crank
  • Stink of raw gas
  • Gas leaking under the engine
  • High oil level
  • Hydro-locked engine

What Causes ATV Flooding?

In many cases, an ATV floods because the engine needs a tune-up, and so if you haven’t serviced your ATV in more than twelve months. A full tune-up now is a great place to start.

Generally, a flooded ATV is a symptom of an underlying problem; it is not the root cause. In this section, we’ll look briefly at some of the more likely root causes of ATV flooding.

They include:

  • Poor maintenance – An ATV should be serviced every twelve months.
  • Incorrect start procedure – Using excessive choke while starting, especially when the engine is warm, can lead to flooding.
  • Faulty choke – A choke manual or auto that’s sticking in the “On” position may also cause hot start flooding.
  • Clogged air filter – A dirty air filter is close to the top of this list for a good reason. A blocked filter causes a rich fuel condition and flooding.
  • Bad gas – Old gas goes stale and loses its ability to ignite. This may result in flooding of the cylinder and spark plug fouling.
  • Fouled spark plug – A spark plug that doesn’t fire won’t ignite the gas, and the most common cause of a nonfiring plug is fouling.
  • Battery fault – While many bikes will run with a low battery, starting may cause some issues. A strong battery is required in order to achieve at least 400 rpm. That’s important for two reasons, sufficient RPM is needed to generate a strong spark, and secondly, a min of 400 rpm is required to create sufficient compression in the combustion chamber.
  • Faulty carburetor – A common carburetor over-fueling fault is caused by an incorrectly adjusted float height. Another common issue is a worn and leaking carb needle valve. These types of carburetor faults are associated with hydro-locking.
  • Mechanical issue – Low compression will result in a no-start, and a no-start means gas is flooding the engine.
  • Electrical issue – A bad plug cap, coil wire, coil, Stator, CDI module, and pickup are all possible causes of flooding.

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Diagnosing The Cause Of ATV Gas Flooding

As we’ve seen in the previous section, the list of possible causes is wide-ranging. In this section, we’ll attempt to diagnose the root cause. It makes sense to check the most common and also easy to check items first, before checking the less likely issues and harder to test. And so that’s what we’ll do next.

Go ahead and check the following:

  • Starting procedure – This may seem insignificant, but if the bike is new to you, the starting procedure may be different. The fix – check your owner’s manual for the correct ignition system and choke use (if manual choke fitted).
  • Air filter – A choked-up air filter will prevent airflow and, conversely, will flood the cylinder with gas. The flood of gas compounds the problem by fouling the spark plug. The fix – remove, check, and clean the air filter. It is common to oil ATV foam filters, but air filter oil should be used, not engine oil. Never wash or oil a pleated paper air filter.
  • Spark plug – The spark plug should be cleaned and the gap checked every three months. The plug should be changed every two years, and check your plug type is correct. Spark plugs are specific to your engine. The fix – remove, check the gap, and clean or fit a new plug.
  • Check fuel quality – Poor fuel quality is a very common cause of no starts, likely the most common cause. If your gas is older than a couple of months, there’s a very good chance your fuel is stale and is fouling the plug, causing a no-start and flooding. The fix – drain the gas tank, and carburetor bowl and use fill with fresh gas. Adding a gas stabilizer helps keep gas fresh for twelve months.
  • Check compression – Low compression is at the bottom of the list as it’s less likely and harder to diagnose and fix. To diagnose successfully, you’ll need to run a compression test, and you can check that procedure here.

How To Un-Flood ATV Engine

ATV throttle

When it comes to clearing a flooded ATV engine, we have three options:

1 Open throttle – Fully open the throttle, but leave the choke off; now, crank the motor over. The open throttle increases airflow to the engine and helps dry out the cylinder. If the engine doesn’t clear and start after two or three attempts, I’d try one of the other strategies below. Excessive cranking will run the battery down.

ATV Choke

2 Wait – Simply walking away and allowing time to dry out the cylinder usually works. Waiting anywhere from fifteen minutes to a half-hour does the job.

That said, if there is an underlying problem causing the flooding, then you may be visiting this problem again before long. Remember, when starting a flooded engine, don’t add any choke.

3 Clear cylinder – Clearing the cylinder will require a few tools and a little effort. You’ll need a plug wrench and a shop rag.

The process is as follows:

  • Go ahead and remove the spark plug
  • Disable the coil by removing the coil power feed. (failing to disable the coil risks fire and also risks overloading the coil)
  • Place a shop cloth over the plughole
  • Crank over the engine to expel the raw gas

Now go ahead and clean, gap the spark plug, and refit.

Mechanics Tips To Prevent ATV Gas Flooding

Spark plug

Here are my top tips for keeping your ATV in great shape and free from flooding

  • Tune-up your engine
  • Turn off Petcock (gas tap) when bike not in use
  • Use a gas stabilizer
  • Clean and gap spark plug regularly
  • Check spark plug is correct heat range

When storing your ATV, it pays off handsomely to pay particular attention to the fuel system.

  • Use gas stabilizer – Fill the gas tank before winterizing your ATV and add a gas stabilizer to the gas tank. Run the engine a while to distribute the mix throughout the fuel system.
  • Use battery maintainer – use a smart battery charger to keep the battery in top shape.
  • Turn off the petcock when the ATV is not in use
  • Park bike undercover and but use a breathable cover

You may find the following posts helpful:

ATV carburetor flooding

ATV won’t start after washing

ATV won’t jumpstart


I wrote a ton of ATV repair guides. Hopefully, you won’t need them, but if you do, we have you covered.

ATV Repair Guides