2017 KTM 150SX Smokes on Startup: Causes – and Fixes

Shop parts for a 2017 KTM 150SX Dirt Bike.

Understanding Startup Smoke on the 2017 KTM 150SX

Seeing smoke from your 2017 KTM 150SX when you first fire it up can be concerning, but it isn’t always a sign of trouble. Knowing when smoke is normal and when it signals a problem is key to keeping your bike running strong. This guide breaks down the most common causes of startup smoke on the 2017 KTM 150SX and offers practical fixes for each scenario.

When Is Smoke Normal?

  • Cold Starts: A brief puff of smoke is common when starting a cold engine, especially after the bike has been sitting. This is often due to condensation or a small amount of excess oil burning off.
  • After Long Storage: If your KTM 150SX has been parked for a while, oil can settle in the crankcase or exhaust, leading to temporary smoke on the first startup.

In these cases, the smoke should clear up within a minute or two as the engine warms up and burns off any residual oil or moisture.

Common Causes of Excessive or Persistent Smoke

If your 2017 KTM 150SX continues to smoke after warm-up, or if the smoke is thick and persistent, it’s time to investigate further. Here are the most likely culprits:

  • Premix Ratio Issues: Using too much two-stroke oil in your fuel mix is a leading cause of excessive smoke. The 150SX requires a precise premix ratio. Too much oil leads to incomplete combustion and visible smoke.
  • Oil Pooling in the Crankcase: If the bike sits for extended periods, oil can seep into the crankcase or exhaust. This pooled oil burns off at startup, causing smoke. If this happens regularly, it may indicate a worn seal or gasket.
  • Worn or Leaking Crank Seals: Crank seals keep transmission oil and air separated from the combustion chamber. If a seal fails, transmission oil can enter the engine and burn, producing thick, white or blue smoke that doesn’t go away as the bike warms up.
  • Carburetor Issues: An overly rich fuel mixture (too much fuel, not enough air) can cause the engine to smoke. This is often due to a stuck float, dirty jets, or incorrect carburetor settings.

Diagnosing the Type of Smoke

  • Blue or White Smoke: Indicates burning oil. This is typical for two-stroke engines like the KTM 150SX, but excessive amounts suggest a problem with premix ratio, crank seals, or oil pooling.
  • Black Smoke: Points to a rich fuel mixture. This is less common but can occur if the carburetor is out of adjustment or the air filter is clogged.

How to Fix Startup Smoke on the 2017 KTM 150SX

  1. Check Your Premix Ratio
    • Drain the fuel tank and refill with the correct oil-to-gas ratio as specified for the 2017 KTM 150SX.
    • Use a quality two-stroke oil designed for high-performance dirt bikes.
  2. Inspect for Oil Pooling
    • Remove the spark plug and check for oil fouling.
    • Look inside the exhaust for signs of pooled oil. If present, clean the exhaust and monitor for recurrence.
  3. Examine Crank Seals
    • If smoke persists and smells like burning transmission oil, inspect the crank seals for leaks.
    • Replacing crank seals is a more involved job, but it’s essential for preventing further engine damage.
  4. Adjust the Carburetor
    • Check the air filter and clean or replace if dirty.
    • Inspect the carburetor for stuck floats or clogged jets. Adjust the air-fuel mixture to factory settings for the 2017 KTM 150SX.

When to Take Action

  • If smoke is light and disappears quickly, it’s likely normal.
  • If smoke is thick, persistent, or accompanied by poor performance, investigate the causes above.
  • Unusual smells, oil loss, or repeated fouled spark plugs are signs that repairs may be needed.

Keep Your 2017 KTM 150SX Running Clean

Startup smoke on the 2017 KTM 150SX is often harmless, but persistent or excessive smoke deserves attention. By checking your premix ratio, inspecting for oil pooling, monitoring crank seals, and keeping the carburetor in tune, you can keep your bike running clean and strong. Regular maintenance and prompt attention to changes in exhaust smoke will help you enjoy more trouble-free rides on your KTM 150SX.

Related Shopping Categories

Shop Oil for a 2017 KTM 150SX Dirt Bike.

Shop Spark Plugs for a 2017 KTM 150SX Dirt Bike.

Shop Carburetor Accessories for a 2017 KTM 150SX Dirt Bike.

Shop Gaskets for a 2017 KTM 150SX Dirt Bike.

Shop Air Filters for a 2017 KTM 150SX Dirt Bike.

Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.