Smoke from the motorcycle exhaust can be from multiple reasons and can also cause a lot of confusion and fear among motorcycle owners. Motorcycle smoking from the exhaust is pretty easy to spot and with the correct repair and maintenance, the smoking can be stopped.
Motorcycle smoking from the exhaust because of worn piston rings, valve seals, or blown head gasket causes the oil or coolant to find its way inside the combustion chamber to get burned, resulting in white, grey, blue, or black color of smoke from the exhaust. Replacing these parts will stop the motorcycle from smoking.
Cleaning clogged air filter, fuel return line, and fuel injector, or properly tuning the bad carburetor will fix the air-fuel ratio mixture and stop the motorcycle from smoking.
So we will go into detail about each of the causes of motorcycle smoking from the exhaust and how to fix it to avoid further damage to the motorcycle’s engine.
We will also discuss the color of smoke coming out of the exhaust and what each smoke color indicates something wrong going on with your motorcycle.
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What Causes Motorcycle Smoking From Exhaust?
There are multiple reasons which can cause the motorcycle to smoke excessively and not fixing them can cause a significant amount of damage to the engine.
So we will explain each cause for motorcycle smoking from exhaust in detail and which damaged or worn part of the motorcycle can be causing it.
1. Worn Piston Rings Cause Motorcycle Smoking From Exhaust
The piston ring’s job is to carry away the heat from the pistons while also maintaining an airtight (compression) seal between the combustion chamber and the crankcase where the engine oil is present.
Over time the piston rings might get worn out depending on your riding style.
Worn piston rings won’t be able to hold an airtight seal which can cause the engine oil to get past the pistons inside the cylinder into the combustion chamber.
Due to these worn piston rings, an excessive amount of engine oil will get inside the combustion chamber where it will get burned along with the air-fuel mixture causing the motorcycle to smoke.
If your motorcycle is burning oil at an excess amount and want to know how to fix it and avoid engine damage then please check the article. ( Click the Underlined Linked To Read )
2. Worn Valve Seals Cause Motorcycle Smoking
Every motorcycle has Intake Valve and an Exhaust Valve. Inlet Valve lets the air-fuel mixture get inside the combustion chamber for the combustion process.
The exhaust gases created from the air-fuel mixture getting ignited by spark plugs will be ejected from the Exhaust Valve.
The valve seals also known as the valve stem seals that sit on the topmost part of the valve stems. Camshaft controls the opening and closing movement of the intake and exhaust valves.
So to keep the whole operation fluid and friction-free, engine oil circulates inside the engine to the moving parts of the engine well lubricated.
A worn or cracked valve seal will let the circulating engine oil get inside the combustion chamber.
This oil will get burned inside the combustion chamber with an air-fuel mixture causing the motorcycle to smoke from the exhaust in an excessive amount.
3. Blown Head Gasket Cause Motorcycle To Smoke
The head gasket is located between the cylinder head and the engine block and it acts as an air-tight seal to not let engine oil or coolant get inside the combustion chamber.
Damage to the head gasket is caused by repeated engine overheating and riding under high engine temperature for a prolonged time or the wear caused to the engine over time.
Once there is a crack or any damage to the head gasket that could compromise the air-tight seal, engine oil or coolant will enter the combustion chamber where it will get burned.
Coolant or oil entering the combustion chamber because of a blown head gasket will cause motorcycle smoking at an excessive amount.
4. Clogged Air Filter Or Fuel Injector Cause Motorcycle Smoking
The air filter acts as a barrier and strainer, which catches debris and dirt particles from the air and allows them to pass through as refined air to the engine.
Over time there will be a buildup of debris and dust particles on the air filter. Not cleaning the air filter will cause a drop in the air supply to the engine because of the dust buildup.
Because of the low supply of air to the engine, the air-fuel mixture ratio gets imbalanced where the motorcycle runs too rich. ( high amount of fuel)
Hence due to a clogged air filter, the air-fuel mixture gets imbalanced and burns a higher amount of fuel causing the motorcycle to smoke from the exhaust with some unburned fuel.
And you can also check the fuel injector to see if the injector is spraying the fuel properly and clean any carbon deposit if necessary for your motorcycle to run properly and not smoke.
5. Wrong Carburetor Jetting Cause Motorcycle Smoking From Exhaust
For carburetor motorcycles, the Pilot Jet and Main Jet dictate how your motorcycle is getting its fuel supplied.
The wrong size of the main jet may restrict or supply more than an adequate amount of fuel which can cause an imbalance in the air-fuel ratio.
The wrong setting of the pilot screw and mixture screw will also cause an imbalance in the air-fuel ratio causing the motorcycle to run a lean or rich mixture resulting in motorcycle smoking.
What Does Each Color Of Smoke From Motorcycle Exhaust Mean?
The color of the smoke coming out of the exhaust can tell a lot about what’s causing it and the worn-out motorcycle part contributing to it.
White Smoke Coming Out Of The Exhaust?
When your motorcycle ejects an excessive amount of white smoke from the exhaust, it means that the coolant or some amount of engine oil is getting inside the combustion chamber.
Cracked/worn valve seals, piston rings, or head gasket causes the coolant or engine oil to find its way inside the combustion chamber.
Black Or Grey Smoke Coming Out Of The Exhaust?
Black or grey smoke coming out of the motorcycle exhaust indicates that the motorcycle is burning an excessive amount of fuel due to an overly rich fuel mixture.
This can be caused due to clogged air filter, leaking/clogged fuel injector, clogged fuel return line, or wrongly tuned carburetor.
Blue Smoke Coming Out Of The Exhaust?
Blue smoke from the exhaust simply means the engine oil is finding its way inside the combustion chamber and getting burned with the air-fuel mixture.
Engine oil gets inside the combustion chamber due to cracked/worn piston rings, worn valve seals, or cracked/blown head gasket.
How To Stop Motorcycle Smoking?
Replacing worn-out parts such as piston rings, valve seals, and head gasket will stop motorcycle from smoking.
Other uncommon causes such as clogged air filters, fuel return line, or bad carburetor tuning will also cause motorcycles to smoke. So cleaning the fuel system, and air filter will stop the motorcycle smoking from the exhaust.
Not changing or cleaning these parts will continue to cause an imbalance in the air-fuel ratio, and engine oil or coolant will likely enter the combustion chamber through worn-out parts such as piston rings and valve seals.
If you avoid the motorcycle smoking problem and keep riding, it will eventually damage the engine.
The performance output and the mileage per gallon (also per liter) of fuel/gas will be lowered.
If you can’t tune the motorcycle carburetor then please take it to the professional mechanic to do it for you.
For fuel-injected motorcycles, check the fuel injector to see if it’s spraying the fuel properly or if something is restricting the flow of the fuel/gas.
Motorcycle Exhaust Smoke FAQ
Motorcycle White Smoke on Startup?
White smoke during motorcycle startup means the moisture from the environment collected overnight in the exhaust manifold getting vaporized due to the exhaust system’s change in temperature from cold to hot.
Motorcycle Smoking After Sitting?
Motorcycle continuously smoking from the exhaust after sitting for a long time indicates either the engine oil or coolant is getting burned inside the combustion chamber or the motorcycle is running a rich air-fuel mixture.
How To Stop White Smoke From Bike?
To stop white smoke from the motorcycle you will have to replace worn piston rings, valve seals, or blown head gasket which are causing the engine oil, coolant, or water to get inside the combustion chamber to get burned.
