Small Engine Lookup

Lawn mower engine smoking: white, blue or black smoke

Reviewed 7 primary sourcesSee sources

The color tells you what is burning. White or blue smoke means oil is burning; black smoke means too much fuel and too little air.

Checks in order

  1. Was the mower tilted?

    Tipping the mower on its side, storing it tilted or mowing a slope steeper than 15° can let oil into the cylinder. Return it to level ground; Briggs & Stratton says the smoke should clear within a few minutes. When tilting, keep the spark plug up or the muffler side down.[1]

  2. Check the oil level and grade

    Overfilling the crankcase or using the wrong grade causes white or blue smoke. Drain to the correct level and use the grade in your manual.[1]

  3. Black smoke: check the air filter first

    Briggs & Stratton’s order is the air filter, then the oil level, then fresh fuel, and only then the carburetor.[2]

  4. Just out of storage?

    Honda says a little smoke at start-up is normal if the cylinder was oiled for storage. Honda GX manuals also note that excess oil left in an oiled foam air filter makes smoke at first start.[3][4]

What the symptom can point to

White or blue smoke that keeps coming

Persistent oil smoke can point to a blocked crankcase breather or breather tube, a crankcase air leak, a blown head gasket, or worn cylinder and rings.[1][7]

Black smoke that keeps coming

Kohler lists black, sooty exhaust as a sign of a rich mixture, such as a clogged air cleaner or a partly closed choke. Honda lists black exhaust as a symptom that can affect emissions and needs a dealer inspection.[7][5]

When to stop and book a repair

Related

Sources

Facts on this page are restated from the documents below and linked to the publisher. Check the document for your exact model before relying on a value.

  1. Why is my engine emitting white or blue smoke?Briggs & Stratton · Causes list and troubleshooting steps · retrieved
  2. Small engine problem solving tipsBriggs & Stratton · Starting, carburetor and exhaust-smoke sections · retrieved
  3. Owner’s manual GCV160 · GCV190American Honda Motor Co. · 00X37Z8B 0029 · English section: safety pp. 5–7, fuel and oil p. 7, maintenance p. 8, problems pp. 9–10, specifications pp. 10–11 · retrieved
  4. Owner’s manual GX120 · GX160 · GX200American Honda Motor Co. · 00X37-Z4H-6100 · English section: fuel and oil p. 8, reduction case p. 10, air cleaner pp. 11–12, spark plug p. 12, problems p. 15, specifications pp. 18–19 · retrieved
  5. Owner’s manual GCV170 · GCV200American Honda Motor Co. · 00X37Z9V 0004 · English section: fuel p. 9, oil and maintenance p. 10, problems p. 12, specifications and emissions symptoms p. 13 · retrieved
  6. XT650, XT675, XT775 owner’s manualRehlko (Kohler engines) · 14 590 36 · Safety p. 2, high altitude p. 4, oil chart and maintenance p. 5, fuel p. 6, spark plug and air cleaner p. 7, troubleshooting and specifications p. 8 · retrieved
  7. XT series service manualRehlko (Kohler engines) · 14 690 01 Rev. G · Identification p. 5, troubleshooting guide pp. 13–14, carburetor causes p. 20, spark plug table p. 27 · retrieved

Primary publishers: Briggs & Stratton, American Honda Motor Co., Rehlko (Kohler engines). Spotted an error? Email the address in the footer with the model and the document you are using.