Is My Choke Open or Closed? How to Tell is Revealed Here

Most lawn mower manufacturers include on their machines, decals which provide step by step instructions on various starting procedures, such as how many primes are required for a push bulb, etc. The problem is that more often than not, these decals degrade and fade over time, due to sun exposure, wear and tear or, their simply not provided at all. To build on our previous post on how to use a choke, found here: How to use a Choke: Mastering the Choke Function in Small Engine Operation it may be a challenge to know when in fact your choke is opened or closed. Or, how to decipher the meaning behind choke symbols found on your unit.

An easy way to resolve this potential problem is by using the following depictions:

Always move the choke lever to the CLOSED position to start the machine.

Think of a choke as a door; This is the symbol for choke CLOSED

In fact this symbol may be found on your unit and think of the choke plate (or door) as preventing air from passing through a channel into your engine. Although it may seem counterintuitive to close the choke on cold start up, it becomes more clear when you consider the influence of air pressure and areas of high and low pressure. Inside the engine, the space within the cylinder is at a lower pressure than the atmospheric pressure surrounding the outside of the engine. So when you pull the start rope, and the piston moves down on its intake stroke, the lower pressured air inside the engine cylinder causes the higher atmospheric pressure surrounding the engine, to rush in through the carburetor to equalize this difference in pressure. In doing so it creates the necessary vacuum to pull the air and gas mixture necessary to start the engine. So in summary, To start a cold engine move your choke plate to CLOSED position. Your unit may have a symbol similar to the one above as it is universal. Move your choke lever or handle to this closed position, look for something similar to the symbol above.

This depicts a closed choke creating vacuum in an engine, outside higher pressure air is drawn into the lower pressure area within the engine.

Once your engine has begun running, open the choke gradually. There are partial positions between completely closed, as shown above, partially open, and completely open. After allowing the engine to run for a brief time (depending on outside temperature) approximately 10 seconds should suffice. Next, open the choke completely to run the machine at maximum speed. The enriched air and gas mixture needed for starting, and the vacuum required to pull it into the cold engine is no longer necessary. Thus, the choke plate can remain opened.

This depicts an open choke in the RUN position.

Again, picture the choke as simply a doorway controlling how air and fuel enters your engine. Keep it closed to start, and open it fully to run. Look for symbols similar to the ones shown above and the good news is these principles apply to all small engine applications! Whether your starting a weedeater, snow thrower, chainsaw, edger etc. this rule remains the same. Your now well on your way to starting your unit with confidence!

Never the Norm!