The Choke

by Had Robinson

The Walbro WG-8 carburetor has a choke.  The other major Walbro carburetor used on paramotors, the WB-37, does not have a choke.  Some engines, like the Thor 130, use the WG-8 carburetor but have no method of operating the choke while in the air.  If you engine is like this, run a piece of glider line from the choke lever down to the bottom of the frame and tie it off so in case you ever need to apply the choke while in the air, you can (see below for why).

The purpose of the choke is to enrich the fuel-air mixture entering the engine when it is cold and, typically, an attempt is made to start it.  In the photo below the choke is fully open.  The air box does not have to be removed in order to determine the choke position.  If the choke lever is parallel with the carburetor body (horizontal), the choke is fully open and is of no effect. 

WG-8 carb showing choke

When is it useful to enrich the fuel-air mixture?  The most important use of the choke is to stop the engine in case the kill switch does not work.  Fully closing the choke will flood and stall a warmed up engine.  The choke, in this way, becomes a secondary tool that can be used to prevent an accident.

The choke can also be used to help start a cold engine.  However, priming the engine correctly works faster and better than choking it and will be less prone to cause flooding.

To use just the choke to help start a cold engine, pull down on the choke knob to fully close the choke.  Pull the starter.  You may have to pull it many times because the carburetor may not have any fuel in it and it will take a while for the fuel pump to do its job.  At some point, the engine will start to turn over on its on.  The moment this happens you must open the choke a little or the engine will stop (stall from flooding).  That is, you will have to move your hand very quickly to open the choke before the engine stalls.  At the same time, a small amount of throttle must be applied.  Once the engine is running smoothly, the choke can be fully opened.

If you forget and leave the choke mostly closed, the engine will flood when the throttle is opened further, such as when launching.  This is why it is always better to prime the engine because the choke is not needed.

What if you shut down the engine while in the air long enough for things to cool down?  How will you prime it while flying?  This is another use of the choke when you need to restart the engine (if you do).

Remember:  Always check to be sure the choke is fully opened after you start the engine and it is running smoothly.  You will only notice a partially closed choke when going to full throttle such as when launching and the engine will flood and either slow down greatly or stop.

Turkey Vulture

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