While a chain saw does produce some heat while in use, it should never overheat or begin smoking. Overheating and smoking are obvious signs of an underlying problem and are an indication that you should shut off the chain saw immediately and investigate the situation before further use. The most likely causes of smoking and overheating are a lack of air and/or a lack of lubrication to the engine or the chain saw chain guide bar.
Lack of Air Flow
When the air that reaches the chain saw's engine is insufficient, it becomes prone to overheating. You may also notice that the chain saw loses power during operation. To ensure that enough air reaches the chain saw's engine, remove the air filter and clean or replace it, depending on the manufacturer's instructions. To clean the filter, tap it a couple of times against a stationary object to dislodge dirt and debris. Immerse the filter in warm, sudsy water for a thorough cleaning and let it air-dry before reinserting it into the chain saw.
Poorly Adjusted Idle
When you see a noticeable amount of smoke emanating from the exhaust while the chain saw is idling, it's time to adjust the machine's engine idle speed. Exhaust smoke indicates that the machine is idling at too rapid a speed. To lower the idle speed on many models of chain saws, locate the low-speed adjustment screw and turn it clockwise until the idle speed slows. Then turn the screw backwards 90 degrees and increase the throttle to ensure that the engine accelerates smoothly. Adjusting the idle speed should remedy the expulsion of smoke from the exhaust. If necessary, adjust the idle-speed adjusting screw as well.
Excessive Amount of Oil
An abundance of smoke emanating from the engine often indicates that an excessive amount of oil has been introduced into the oil and gasoline mixture that powers the chain saw. Ensure that you're mixing the correct amount of oil and gasoline according to the dictates of your owner's manual. Empty the fuel tank of all the oil and fuel mixture and fill the tank with the newly mixed fuel and oil before using the chain saw again.
Chain and Guide Bar Issues
If you notice smoke and heat coming from the bar and chain area, the culprits are usually easy to diagnose. Immediately check the guide bar oil reservoir to ensure that it contains oil to cool and lubricate the chain and bar and that it hasn't run dry. If the reservoir contains oil, run a quick test to ensure that the oil is exiting the reservoir and reaching the chain. Point the tip of the chain saw blade at a light-colored surface and allow it to run at full throttle for 45 seconds. Examine the surface afterward to look for a light line of oil made up of small dots to prove that the oil is emerging from the reservoir. Last, but not least, check the tension of the chain on the bar to ensure that it's not adjusted too tightly. If you can't advance the chain forward manually, loosen the tension slightly.