I was asked the question the other day, why does my motorcycle keep backfiring? There isn’t one single answer to this question. There are many variables when discussing the cause of a motorcycle backfire. I have gathered up all the information I could find on the subject and I hope it helps you gain some knowledge as well as that lost power!
Why Is My Motorcycle Backfiring?
A motorcycle backfires when the motorcycles engine is experiencing an emission system malfunction, resulting in a mistimed explosion in the cylinder or exhaust. This occurs commonly when the engine is running rich, running lean or has an exhaust leak.
The sound of a backfire can be startling to the unexpected ear and worrisome or annoying to the motorcycle owner. A backfire is an explosion that happens within the intake or the exhaust of your motorcycle. This explosion is meant to take place in the combustion chamber of your engine and when it doesn’t, this causes an interruption in the engines function. I like to think of it as skipping a heart beat. This occurrence can result in a flame emitting from the exhaust as well as a LOUD popping sound.
Motorcycle Backfire Vs. Afterfire?
What Causes a Motorcycle Backfire?
A motorcycle backfires when the motorcycle is experiencing an emission system malfunction such as: running rich, running lean or has an exhaust leak. There are a few other things that can cause a backfire such as: weak or bad fuel pump, low fuel pressure, clogged fuel filters or anything that might cause an unbalance in the air-to-fuel ratio. Many people like to modify their bikes with a new exhaust for better performance or sound BUT this comes at a risk. The stock muffler on a motorcycle is specifically designed to ensure the motorcycles engine runs the way it is supposed to. When you change out the exhaust it can cause an unbalanced air-to-fuel ratio, resulting in backfiring. In this case it is usually caused by increased airflow going into the motorcycle.
Difference Between Rich and Lean?
Rich:
When an engine is running too rich this means that there is more fuel present in the combustion chamber than there is air. Without enough air in the combustion chamber the explosion to drive the pistons will not occur. This will cause excess fuel to pass into the exhaust and go BANG!
Lean:
when the engine is running too lean this means the opposite of rich; there is more air than there is fuel in the combustion chamber and is basically starved of fuel.
When either of these happen the fuel may find its way into your exhaust and explode from the heat of the exhaust. This will cause the loud popping explosion you hear.
Is a Backfire Bad For My Motorcycle?
The simple answer is YES. Backfiring is bad because it is a fuel ratio malfunction and will result in a loss of power. Sometimes you can really feel the cut out of power for a brief moment. Running the motorcycle too rich or too lean can also cause the internal temperatures of the combustion chamber to get too hot and fry your engine! Uh Oh!
Bad Spark Plug:
One of the easier things to check off the list would be the spark plug. The spark plug is responsible for the ignition and it might have bad ignition timing with the compression.
Gasoline:
Sometimes the issue can be as simple as the levels of Octane in your fuel. I recommend running a higher-octane fuel through the engine to help clean out the fuel system and possible put a halt to those backfires. I recommend always using a premium high octane fuel for your bikes.
Dirty Carburetor:
This applies to engines that use a carburetor for its fuel management system instead of fuel injection. If your motorcycle has sat for a lengthy amount of time then it is very possible the old gas has sat in the carburetor and the impurities have settled, causing a clog and your engine to run poorly or maybe not run at all.
Jets:
Your carburetor has 4 components inside that make all the magic happen when you get a hand full of that whiskey throttle. These can get filled with dirt and “gunk” preventing them from functioning as they should.
- Pilot Jet – this controls the amount of fuel when idling
- Main Jet – this controls the fuel when you open up the throttle (between 50 and 100 percent power)
- Jet Needle – this controls the fuel when you open and close the throttle (between 20 and 80 percent power)
- Needle Jet – this is what the jet needle pops in and out of (between 15 to 60 percent of throttle
How to clean the carburetor:
If you think that you need to clean the carburetor then you need to go buy a can or 2 of carburetor cleaner, it will come in a spray can with a straw attachment. 
- Wash the bike, especially the engine and carburetor exterior
- TAKE PICTURES: everyone always thinks they will remember exactly where everything goes (myself included) but this just isn’t the case 100% of the time. When it comes to something with several connections and moving parts, it’s smart to snap a few quick pics for reference if needed.
- You need to remove the carburetor from the bike and drop the fuel from the float bowl.
- All the housing and the jets inside should be removed and cleaned by spraying them thoroughly with the carburetor cleaner.
- Clean the air filter (should be doing this regularly) lube it and seal it with a thin layer of grease to the air box housing.
- Wipe out the air duct leading towards the carburetor.
- Put it all back together while keeping everything very clean!
If you have done all of this and are still experiencing backfiring problems then you more than likely have an air flow issue. On many older carburetors there are idle and mixture screws that could also need adjusting. If you have an aftermarket exhaust I would try swapping the stock exhaust back on the bike and see if the backfiring persists.
How to check for an exhaust leak:
There are a few different methods you could go about checking for an exhaust leak. If you have access to a smoke machine then here is a video demonstrating how to perform that method. If you don’t have access to a smoke machine, a very popular method is to use dish soap and water. I recommend you use a squirt bottle and soak the connections throughout the full exhaust system; headers, muffler slip on and welds. Start up the bike and look around those connections for bubbles building up.
I hope this was informative and helped you pursue a fix for your backfiring problem or curiosity. Comment below and let me know if I helped you out! Stay on the throttle my friends!
Go check out my article on the best goggles in 2019!