Symptoms
- Engine runs rough or knocks after refueling
- Excessive smoke after a recent fill-up
- Engine seized or seizing shortly after using new fuel
- Poor power and overheating after switching fuel sources
Likely causes
- CommonAccidentally used straight gasoline with no oilThis is the most damaging mistake for a 2-stroke engine, since it relies on the mixed oil for lubrication.
- CommonIncorrect oil-to-gas ratioToo little oil causes lubrication problems; too much causes fouling and smoke.
- PossibleOld fuel used well past its useful shelf lifeDegraded fuel burns poorly and can leave gummy deposits.
- Less commonWrong fuel type such as diesel or E85Using an incompatible fuel type can cause immediate and severe running problems.
What to do
- Stop running the saw immediately if you suspect the wrong fuel was used, to limit any damage.
- Drain the fuel tank completely and dispose of the bad fuel properly, never down a drain or onto the ground.
- Flush the fuel system if possible with a small amount of correctly mixed fresh fuel, running it briefly and draining again.
- Refill with properly mixed fuel at the exact ratio specified in the owner's manual, typically 40:1 or 50:1 for chainsaws.
- Check the spark plug for fouling or unusual wetness and clean or replace it.
- Run the saw briefly at idle first to check for abnormal noises before returning to normal use.
- If the saw ran on straight gas for any meaningful time or shows signs of seizing, have a small-engine shop inspect the internal engine for damage.
Tools and parts
- Fuel mixing container
- Spark plug wrench
2-stroke oilSearch: “2-cycle chainsaw engine oil”
Spark plugSearch: “chainsaw spark plug replacement”
When to call a pro
If the saw shows signs of seizing or ran on incorrect fuel for an extended time, have a small-engine shop check for internal damage before further use.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.