White, bluish-white, and black-colored smoke can indicate some serious problems with your motorcycle engine.
The first section of this article will examine the common reasons a motorcycle blows white smoke. The second section looks at the various reasons a motorcycle blows black smoke.
Reading both article sections, the reader will learn how to recognize and solve the problems that cause motorcycles to blow white or black smoke before they cause severe motorcycle damage, including total engine failure.
Reasons Motorcycle Blows White Smoke
Here are reasons a motorcycle produces white smoke:
1. Moisture or Condensation Burn Off After Cold Start
The most common reason a motorcycle blows white smoke during a cold start is due to residual condensation, humidity, or moisture in the tailpipe.
When you start your bike in the cold, the condensation residue in the pipe heats up and steams out of your exhaust as white smoke.
- White exhaust smoke caused by condensation should only last 30-40 seconds.
- Once the moisture residue turns to steam and blows out of your motorcycle’s tailpipe as white smoke, there should be nothing left in the pipe to burn, and your exhaust smoke should return to its usual color and consistency.
If your exhaust pipe continues shooting white steam after a minute of running, you have a more significant problem on your hands than moisture in your pipes.
Also, read our article about motorcycle cold start problems.
2. Blown Head Gasket
Coolant can leak into your engine chamber if your motorcycle has a blown head gasket. Once in the combustion chamber, the coolant burns up and is blown out along with the rest of the fuel combustion exhaust. The vaporizing coolant forms white smoke coming out of the motorcycle exhaust pipe.
The presence of coolant in your combustion chamber hinders engine performance and has a negative impact on your combustion rate and piston operation.
- The presence of coolant in your combustion chamber is enough to impact your motorcycle’s performance enough to cause significant engine failure down the road.
- That said, if a blown head gasket is the reason the coolant is getting into your combustion chamber and causing white vapor in your exhaust, the blown gasket is already causing engine damage.
- Burning coolant has a sweet smell, meaning that if your bike’s white exhaust smoke smells sweeter than usual, the presence of coolant in your engine is likely the reason.
Your bike’s head gasket seals the space between the engine block and the cylinder head on liquid-cooled motorcycles, preventing liquid coolant from mixing with the fuel or oil.
The primary cause of early head gasket failure on a motorcycle engine is the deformation caused by overheating an overworked engine.
- The overworked machine overheats erratically, driving the engine block’s metal to expand irregularly.
- The expanding metal increases the gap between the cylinder block and the head.
- The head gasket expands along with the metal, stretching and blowing out in the process.
You may also notice the presence of coolant in your oil, as a blown head gasket often allows coolant to leak into your oil pan.
For more information about this topic, please read our article about reasons motorcycle smell like coolant.
3. Cracked Cylinder Head
If your motorcycle’s cylinder head is cracked and you have a liquid-cooled motorcycle, coolant or water can leak through the rack and into the engine cylinder. The coolant combusts in the cylinder and is pushed out of the exhaust pipes of your motorcycle as white smoke.
The cylinder head is the very top part of your engine block.
- If your motorcycle engine overheats, its cylinder heads can warp or crack.
- If air leaks into your cooling system, your cooling will become uneven, which also causes racking to metal components like your engine cylinder heads.
Regardless of why your cylinder heads are cracked, your motorcycle is unsafe to ride until the crack is repaired. You risk total engine failure and collisions when you ride on a cracked engine head.
If you suspect a cracked cylinder head is the reason your motorcycle is burning up coolant and blowing white smoke, thank the smoke as a signal not to ride your bike until it’s repaired.
4. Worn Piston Rings Let Oil into Combustion Chamber (Blueish White/Grey Smoke)
Suppose your motorcycle is blowing white smoke with a blueish-grey or silver quality. In that case, it may be because your piston rings are worn out, breaking the only seal between the combustion chamber and the crankcase, particularly on older bikes.
The piston rings seal the space between the top half of the cylinder, the combustion chamber where air and fuel are burned and turned into exhaust smoke, and the bottom half, the crankcase.
- Your motorcycle’s crankcase is doused in motor oil, which squirts against the base of the pistons and various other motor parts to ensure they stay cool and lubricated.
- The piston rings prevent that splashing oil from entering the combustion chamber.
- If the piston rings wear out, the oil can squirt past them and into the combustion chamber, where it is ignited along with the fuel.
- Once ignited, the combusted oil becomes a thick bluish-grey poof of smoke and blows out of your bike’s rear pipes.
The root cause of a worn piston ring is routine wear and tear, which is one reason it’s more common on older bikes.
That said, inspecting your piston rings during routine service will catch the wear before this happens.
If worn piston rings are the reason your bike is blowing blueish-silver-white smoke, oil is burning up in place of fuel, which causes engine performance issues and waste oil.
If the oil level is low, your engine will overheat from a lack of lubrication. The increased friction between the motor parts causes heavy damage, meaning you shouldn’t ride your motorcycle until the worn piston rings are replaced.
Reasons Motorcycles Blow Black Smoke
Here are some reasons motorcycles blow black smoke:
5. Unclean Air Filter
A contaminated air filter can cause black smoke to blow from your motorcycle’s exhaust by preventing the inflow of clean air, causing your motorcycle’s air-fuel mix to run rich with fuel. The excess fuel causes an increase in fuel combustion and thick black exhaust smoke.
Hindering the air intake can cause a rich fuel mix, damaging your bike’s spark plugs and, in time, other engine and exhaust system components.
Additionally, any unburned fuel will combust in the exhaust system, causing popping sounds and hindering engine performance at the very least.
Please also read our article about reasons a motorcycle has a strong exhaust smell.
6. Electronic Computer Unit Needs an Update
If your motorcycle’s ECU needs a flash or an update, your air-fuel ratio may be affected, causing misfiring, stall outs, and an increase in the black smoke emitting from your exhaust pipes.
Modern motorcycles equip an ECU (Electronic Control Computer). The ECU communicates with various sensors across the motorcycle’s systems and regulates air-fuel ignition and exhaust emissions, among other essential functions.
These ECU systems need to be updated during service maintenance. If the ECU flashing falls behind, or its communication with the various sensors is interrupted or inaccurate, your bike’s fuel maps and exhaust systems can malfunction intermittently.
One of the byproducts of these failures is an increase in black smoke emitted from your tailpipes, which may come and go erratically.
7. Failure With Your Fuel Injectors
Suppose one of your motorcycle’s fuel injectors fails or gets clogged with debris. In that case, your fuel system can build up with carbon residue, which is burned up during the combustion process and blown out of your motorcycle tailpipes as recessive black smoke.
A fuel injector’s core function is to shoot fuel into the combustion chamber inside the engine cylinder.
If the file injectors become clogged or wear out, the fuel flow is interrupted, and fuel may even end up in the wrong places, causing thick plumes of motorcycle exhaust smoke.
8. Expired Engine Oil
Burned, contaminated, or old engine oil loses its lubrication properties and cooling effects, causing the carbon deposits in the oil to burn up inside the hot engine, vaporize into thick black smoke, and blow out of your motorcycle’s exhaust pipe.
Check your engine oil immediately and replace it if it looks dark or contaminated. Engine oil needs to be replaced per the service intervals outlined in your bike’s service manual.
9. Worn or Stuck Float Needle (Carbureted Motorcycles)
If a motorcycle is old or sits with fuel in its carburetor bowl for an extended period, the aging fuel can cause the float needle to stick in place.
This allows excessive fuel to flood the carb instead of air. The extra power burns hot and blows out as black smoke.
The float needle is the component that seals the fuel flow into the carb for combustion once it reaches its ideal fuel level.
If the needle is jammed, it won’t rise along with the fuel level, meaning it will allow a continuous flow of fuel into the chamber if it’s jammed.
If the needle wears out, it may just be letting fuel leak past it into the carb.
Regardless, excessive fuel means less air, which means the fuel is burning much hotter and combusting in higher doses.
Any fuel that doesn’t combust will escape into the hot exhaust system and combust, causing misfiring and damage to the engine and exhaust system until the float needle is replaced.