Symptoms
- Visible smoke from the muffler continuously, not just at startup
- Smoke has a strong burning smell
- Engine runs rough along with smoking
- Smoke gets worse the longer it runs
Likely causes
- CommonToo much oil in the fuel mixAn incorrect, overly rich oil-to-gas ratio causes excess unburned oil to smoke out the exhaust.
- CommonNormal light smoke at cold startupA brief puff of smoke when first starting a cold 2-stroke engine is normal and not a problem.
- PossibleClogged air filter causing a rich mixtureRestricted air makes the engine burn more fuel than it should, producing smoke.
- PossibleWorn piston rings or cylinderAn aging engine can burn oil excessively, producing constant smoke.
- Less commonOverheating from blocked cooling finsExtreme heat can cause smoke from residue burning off the engine housing.
What to do
- Drain the fuel and check that you mixed it at the exact ratio specified in the owner's manual, typically 40:1 or 50:1.
- If unsure of the mix, drain and remix fresh fuel at the correct ratio using a marked mixing container.
- Clean or replace the air filter to rule out a restricted air supply.
- Clean debris from the cooling fins and muffler area.
- Run the trimmer briefly and watch whether smoke decreases after the initial warm-up puff.
- If smoke remains heavy and constant after correcting the fuel mix, the engine may be burning oil internally from worn rings.
- Have a small-engine shop inspect compression and internal wear if smoking persists.
Tools and parts
- Fuel mixing container with ratio markings
- Air filter
2-stroke oilSearch: “2-cycle engine oil correct ratio”
Air filterSearch: “string trimmer air filter”
When to call a pro
If the fuel mix is correct and smoking continues heavily, a small-engine mechanic should check compression for worn internal parts.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.