How to Troubleshoot a Chainsaw

Fuel and Oil

Chainsaws have what are called two stroke engines in which the oil and gasoline are mixed together. The ratio of this mix---specified by each manufacturer---must be correct for the engine to run properly and be lubricated adequately. Fuel can become gummy with age and this can wreak havoc on the chainsaw's engine. There are additives or fuel stabilizers that mix with the fuel to counteract this problem and they generally work quite well.

The spark plug, of course, provides the spark that ignites the fuel on each cycle of the engine. If the spark plug gap, as it's called, is not correct, the saw may run poorly. The gap is the small distance between the two electrodes on the plug below the threaded portion where it threads into the engine. Different engines require different plugs with specific gaps that are measured with a gap gauge and set accordingly. In addition to the gap, plugs can become fouled with oil or other deposits, degrading engine performance. Cleaning or replacing the spark plug is the solution to this problem.

The air filter does just what its name states---it filters the air before the air is mixed with fuel and drawn into the engine. Like any other filter it can get clogged, resulting in poor engine performance. A simple cleaning with a stiff utility brush or a gentle blast of compressed air can often make a big difference in improving engine performance. If the filter is in very bad condition it should be replaced.

Anything involving the inner mechanics of the carburetor is really a job for a trained mechanic specializing in small engine repair. There is one carburetor problem, though, that can potentially be addressed fairly easily. The carburetor has needle valves inside with tiny openings for fuel to pass through. If these become gummed up the engine might run poorly or not at all. There are fuel additives specifically formulated to clean these gums and, like fuel stabilizer, they can work quite well if the problem is not too severe.

The bar is the flat, elongated metal part with a track in it that the chain travels around. The track must be free of sawdust and debris so that the chain rides freely in it. Sandwiched inside the bar near its tip is a cog with teeth that catch the underside of the chain as it travels around. This cog helps keep the chain on track and it must be free of debris and turning freely for the saw to operate properly.

The chain itself must be sharp and generally in good condition. Even if all the other parts are working at top performance, a dull chain will, of course, make the saw cut poorly. A dull chain, if otherwise in good condition, can be sharpened. A chain in very poor condition should be replaced.

Chainsaws have a safety feature known as a chain brake. It is engaged via the hand guard immediately in front of the uppermost hand. If the tip of the bar were to contact a log and kick back and up severely enough, the back of this hand guard would be forced against the back of the wrist and pushed forward toward the chain. This can trip a mechanism inside that stops the chain. The chain will remain seized until the guard is pulled back to release this brake. This is a very good safety feature but if it somehow trips unknowingly, an inexperienced operator might be wondering why the chain is seized up.