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How Chain Saws Work


The Choke
Choke open
Choke open

There's nothing to the choke -- it is just a plate that obstructs air flow.

Choke closed
Choke closed

This short video of the choke in operation (0.5 MB) shows just how simple the choke really is. The section later in the article explaining the carb also explains the choke in detail.

Removing the pull-cord assembly reveals a self-contained unit that holds the cord's spool and spring:

Its center shaft fits into two spring-loaded pawls that engage when you pull the cord to start the engine, but otherwise spin freely. The pawls are mounted on the flywheel, shown here:

In the above photo, the flywheel is the aluminum disc on the left with the blades. These blades suck in air and force it back and around the fins on the combustion chamber to cool it. The flywheel also contains the magnets that power the magneto -- the white block on the lower right side of the flywheel. The hole above the magneto is where the carb attaches.

At this point, you can see that we have stripped the saw down to the engine and a top, bottom and front cover plate. Let's look a little more closely at the clutch, magneto and carb before moving on to the engine itself.