When cylinders go bad, gaskets leak or really anything internal on your dirt bike or ATV engine that allows for flawed combustion of fuel or any fluid used for the proper function of a 2-stroke or 4-stroke the telltale sign is usually seen coming out of the exhaust pipe.
Often the bike putters to a stop, other times you can keep riding but at the risk of permanent, not to mention expensive, damage to internal parts or even the whole engine. There's blue smoke, gray smoke, the dreaded black smoke and even white smoke. So what's it all mean?
What Does White Smoke Mean
Let's start with white smoke. Upon the first start of the day expect a little bit of white smoke which is actually water vapor. The good news it's harmless and perfectly normal. Unfortunately, that's as good as it gets. If it doesn't stop after 20 or 30 seconds or any other time you see white or even white smoke with a grayish tint it's bad news.
White smoke is often an indication that coolant is burning usually in the combustion chamber. Remember the 2015 Arenacross Championship when Jacob Hayes T-boned Kyle Regal in an attempt to take Regal out? Well, it backfired as Regal did get thrown off the bike but Hayes fluttered around the track emitting white smoke thanks to a broken water pump. In this case, or in the event of a damaged radiator or broken radiator hose, the white smoke doesn't spew out of the exhaust pipe.
Taking it down a notch, the usual result of burning coolant happens from everyday crashes or just typical wear and tear like:
- A crack in the deck of the cylinder near the coolant jacket or a cracked cylinder head will cause coolant to enter the combustion chamber
- A damaged or blown head gasket will cause coolant to enter the combustion chamber
What Does Black Smoke Mean
Never a good sign. Lots of people confuse black smoke with burning oil; it is, in fact, burning fuel. A number of reasons cause fuel to burn which means the engine in your dirt bike or ATV is operating in a "rich fuel" environment. In simpler terms, the fuel to air ratio is way off. It might be a simple fix or a bit more complicated but problems leading to a rich fuel environment include:
- A leaking or dripping fuel injector, or a leaking carb float needle or seat, or stuck carb float will cause a rich fuel condition
- Broken or cracked reeds (2 Strokes)
- Cracked or poor seating intake valve (4 Strokes)
- Incorrect carb jetting
- Incorrect tuning with electronic fuel injector programmer
What Does Blue (or Blue/Gray) Smoke Mean
Now you have burning oil. But you're in luck if you've got a 2-Stroke. Those engines normally emit a blue/gray smoke. But if it's excessive then you've got a burning oil problem, a rich fuel condition like noted above, a bad spark plug or a malfunctioning power valve. Additional issues causing oil to burn on 2-Strokes or 4-Strokes include:
- Leaking valve seals
- Excessive clearance between the valve stem and the valve guide
- Worn or damaged piston rings
- Worn cylinder walls
- A closed PCV valve
The blue smoke coming from this 2-stroke is actually normal
Also, for dirt bikes equipped with a clutch that uses separate oil than the engine you might have a worn out crankcase seal. In 2-Strokes this is an easy diagnosis because the oil used on the clutch side is not the yummy smelling premix oil thus you'll smell good 'ole engine oil. On a 4-Stroke (usually Honda) the smoke typically blows out of the crankcase vent rather than the exhaust pipe.
When faced with a smoke issue, don't continue riding.
Routine maintenance helps prevent many smoke related issues but old seals or gaskets and certainly a big crash can cause fluid leaks. Fortunately, the color helps narrow down the problem helping you find a solution and back to riding.
Written By: AndrewT