PWK Manual Choke The Little Push That Starts Cold

On a cold morning, however many times you pull the starter, nothing happens until you first push down that small knob. The PWK manual choke is that push: a plastic knob on top for a finger, a stepped plastic shaft below, a hex nut and threaded section in the middle, a metal spring, and a brass needle at the very bottom. It screws into the choke port of the carburetor, and it is ready to work.

How does the choke help a start? A cold engine has walls that are too cool and an oil film too thick, and the normal mixture will not light. The choke narrows the path, changes the mixture until it catches. Press the knob down and the needle advances to restrict; once the engine is warm, let go, and the spring pushes the needle back to the normal opening. No electricity anywhere, just your hand and a spring.

Why so many pieces? The knob is for your finger, the threaded section and hex nut lock it into the carb port with something for a wrench to bite, the spring is the return, and the brass needle is the part that actually chokes. Brass is a soft metal, so it wears the seat gently instead of chipping it, and when it finally gives up, the whole valve is cheap to replace.

When does it go? When the knob will not stay pushed in, the spring is stretched and the needle no longer returns, the tip is worn flat and the choke has no effect, or the thread is stripped and the valve rocks. Fit it with a clean thread, tighten the hex, and check that the needle moves freely and comes back on its own.