A Tutorial On What To Do If Your Motorcycle Engine Is Flooded


When we encounter problems with our motorcycles, it seems to come at the least convenient times. A flooded engine is no exception and it can happen to anyone and their motorcycle.

Though a flooded motorcycle engine isn’t enjoyable to deal with, it’s actually quite possible to take care of it yourself in the comfort of your own garage or driveway with some simple tools.

What should you do if your motorcycle engine is flooded? When your motorcycle engine is flooded, the first thing you should do is wait 15 minutes for the gas in the engine to dissipate. If that doesn’t work, turn off the petcock, remove the ignition coil fuse, remove the spark plugs, place rags slightly inside the spark plug holes, and crank the engine to let the excess gas squirt on the rags.

Out of the several motorcycles I have owned, a flooded engine was no stranger to most of them. I’ve been able to perform this flooded engine fix several times and it has proven to work well. Along with knowing how to fix a flooded engine, I can explain several other things about flooded motorcycle engines that may be helpful in your situation.

How To Fix A Flooded Motorcycle Engine

A flooded motorcycle is an extremely frustrating situation and I have had my fair share of having one. It can also seem a bit scary the first time it happens. The term “flooded engine” doesn’t sound right, in fact it almost sounds detrimental to the motorcycle.

In most cases, a flooded motorcycle engine shouldn’t cause too much alarm. It’s a pretty common occurrence and can easily be taken care of if the right steps are taken. Like I said before, I’ve done this a handful of times myself and started out doing so as an amateur; everything turned out just fine.

If you’ve found yourself with a flooded motorcycle engine, the first thing you should do is stop attempting to start it and let it sit for at least 15 minutes. This will allow the built up fuel inside the engine to dissipate and/or drain.

Some may worry about the built up gas inside a flooded engine draining past the piston rings. When this happens, the gas mixes with the oil that’s inside the engine.

While it’s possible for some of the gas to drain past the piston rings, it’s not too much cause for alarm because the very small amount that does drain and mix with the oil will not be enough to change the consistency of the oil. If you are worried about it, you can change your oil which should take care of the problem.

In rare cases, a flooded motorcycle engine may cause too much gas to drain past the piston rings and mix with the oil inside the engine. If this does happen, that’s due to a faulty piston ring because it shouldn’t be letting that much gas past it. A faulty piston ring would also show the symptom of burning a lot of oil up to the point.

So unless your motorcycle has been burning a lot of oil, you won’t need to worry about the gas seeping into parts of the engine it shouldn’t. While you wait, most of the gas built up in the cylinder will likely evaporate through the open valves.

If you’ve waited at least 15 minutes and attempted to start the motorcycle only to find yourself flooding the engine again or the gas hasn’t seemed to have dissipated, you’ll need to resort to plan B which is emptying the cylinders yourself.

To do this, the first thing you’ll need to do is turn off the petcock. This will prevent adding more fuel to the engine when you go to crank it in a few minutes. The next thing you need to do (and it’s very important you do not skip this step) is to remove the fuse that goes to the ignition coil.

Some say that removing the ignition coil fuse is too much, but I beg to differ. You may still be getting a current from the ignition coil that is running through the spark plug wires. You don’t know what those dangling wires (or dangling spark plugs if they’re still connected to the wires) will touch while you’re fixing this problem and it could result in you getting shocked or possibly grounding to the gas tank.

After you’ve removed the ignition coil fuse, remove the spark plugs and examine their condition. Make sure there is not corrosion and that it has the appropriate electrode gap (the space between the spark plug and the hook at the end of it).

Next, get a few old cloths and slightly place them inside the spark plug holes. It’s important you don’t stuff them in there because when you go to start the engine, the compression will just blow them out and gas will spray. Place them in a way where they’ll be able to catch the spraying gas but there’s also room for air to pass them.

Now you can start cranking the engine. This will cause the pistons to push up and push the gas out of the spark plug holes into the cloth. After a few minutes of cranking the engine, you should be able to take the cloth out of the spark plug holes, replace the spark plugs and spark plug wires, replace the ignition coil fuse, turn the petcock back to “on,” and start your motorcycle.

What Causes A Flooded Engine

You may have encountered a flooded motorcycle a few times throughout the time you’ve owned your motorcycle. Or perhaps you’ve simply heard about other people having the issue. We all know it happens, but a lot of people wonder how a motorcycle engine floods in the first place.

A motorcycle engine gets flooded when the fuel is running into the cylinder correctly but there is no spark to ignite the fuel. So the carburetor or fuel injector (usually a carburetor issue) keeps pushing in more and more fuel but because there is no spark to ignite the fuel, the fuel remains in the cylinder and eventually fills it up or more commonly known as “floods” it.

It eventually gets to a point that even if there was a spark that happened with all that fuel built up, the fuel wouldn’t ignite because the air to fuel ratio is so far off. There literally is no room left for the air to get in to create the appropriate combination needed to create the combustion.

In short, the main reason a motorcycle engine floods is because of faulty spark plugs that aren’t providing the spark the engine needs to combust. Spark plugs are simple parts, but if everything on them isn’t just right it can cause a slew of problems such as this.

The ignition coil as well as the spark plug wires could also be a likely culprit. If the ignition coil is malfunctioning, it won’t send the right signal through the spark plug wires and tell the spark plugs to spark. Similarly, if the spark plug wires are worn or cracked, the current could arc to the frame which prevents the spark plugs from getting a spark at all.

How To Tell If A Flooded Engine Is Your Problem

A motorcycle not starting could be caused by hundreds of reasons, so it’s sometimes hard to know if a flooded engine is your culprit. There are a few specific symptoms that can easily indicate that a flooded engine is your problem.

Obviously, the first symptom will be that your motorcycle won’t start. The starting mechanism will sound perfectly normal, but that the combustion just isn’t happening.

The second biggest sign of a flooded engine is a sudden smell of gas. Because gas is building up in the cylinders, you’ll easily be able to smell it. The third sign to look for is any fuel dripping or spraying out of the exhaust pipe. Some water may have built up inside the pipes, so if they’re spraying any liquid make sure it is gas that it’s spraying.

If you have all three of these symptoms, chances are the reason your motorcycle isn’t starting is due to a flooded engine. There are a few things you can do if you want more visual evidence that your engine is flooding.

Because a flooded engine is due to a lack of spark from the spark plug, you can actually check the spark plugs themselves and see if they’re giving a spark. Remove the spark plug wires from the spark plug then remove one spark plug from the engine and reinstall it in a spark plug wire (so the spark plug and wire are just “dangling”).

You’ll then need to touch the end of the spark plug to the engine or frame (the hook end) so it becomes grounded. Be very careful with where you ground it; you don’t want to ground it near or on any gas or any flammable chemicals. Never ground the spark plug wire on the motorcycle tank.

Once the spark plug is grounded with it still connected to the spark plug wire, go ahead and hit the starter button (with your fingers away from the spark). If the spark plug does spark, you’ll know the spark plug isn’t working. You can try this on all of your spark plugs. If all of them don’t work, you likely have an ignition coil issue. If some work and some do not, you’ll need to replace all the spark plugs.

How To Prevent A Motorcycle Engine From Flooding

Like I said before, encountering a flooded engine is annoying and you probably don’ want to ever deal with it again. There are a few steps you can take in caring for your motorcycle that will prevent your engine from flooding in the future.

The main reason a motorcycle engine floods is because of malfunctioning spark plugs. Spark plug maintenance is key in keeping up with the health of your motorcycle engine. You’ll need to examine your spark plugs at least once a year and replace any if they look less than functional.

A lot of people don’t understand the importance of the spark plug gap at the end of the spark plug (the distance between the spark plug and the electrode at the end, or the hook looking part). People often buy a spark plug from the auto store and place it in the spark plug hole and call it good. While this will work for a while, it won’t be as efficient in the long-run.

When you buy a spark plug, you must set the appropriate spark plug gap at the end of it. You can buy a spark gap tool for a couple of dollars at any auto parts store. You’ll need to look in your owner’s manual or look online about what the appropriate gap space needs to be on each spark plug in your motorcycle and make the appropriate changes to it using your tool. Spark plugs do not come stock set at the right gap specific to each vehicle.

Along with regular spark plug maintenance, you’ll also want to regularly check the condition of your spark plug wires as well. Any cracked or brittle wires should be replaced promptly because any opening in them could cause the current to arc on to the motorcycle itself instead of the spark plug.

Related Questions

How can you tell if your motorcycle engine is seized? If you are sure your battery and starter are in good shape, an electric starter engine will click but will not rotate. On a kick starter engine, the kick pedal will not move at all as it will be stuck in place due to the piston seizure. Click here to see my article for more info.

What are some other reasons a motorcycle won’t start? Some reasons a motorcycle won’t start can include a dead battery, blown fuses, a clogged injector, a bad starter, engine timing is off, or clogged jets in a carburetor. For more information about starting issues, see my article here.

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