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If you’ve ever struggled to start a carburetted motorcycle, moped, or scooter on a cold morning, it’s because carburetors don’t like the cold at all. Thankfully, that’s where the ‘choke’ comes in to save the day. But what is the choke, and how do you use it?
Tune in to discover:
- What the “choke” is
- How it works, and how to use it
- Why it’s called a “choke” to begin with
Hello, and welcome to another episode of 30-minute motorcycling – a podcast for those riders who are at the beginning of their own Dual Wheel Journey, where you’ll discover something new about how your motorcycle, moped, or scooter works – in less than 30 minutes. Have you ever gone out to start your carburetted motorcycle, moped, or scooter, on a pretty cold morning, and all you hear is something like this: [sound of bike not starting] Then, you check everything, but everything checks out – there’s fuel in the tank. The killswitch is turned to the “Off” position. The sparkplugs are clean. And yes, the petcock or fuel tap is set to “On.” And yet, the engine won’t start. In that case, have you tried the choke? In this episode, you’ll discover what the choke is, what it does, and how to use it. But first, let’s talk briefly about the carburetor. The job of the carburetor is to let in enough air and fuel into the combustion chamber so the engine can ignite and harness the energy from the combustion inside – hence, why it’s known as an “internal combustion engine.” However, one flaw of a carburetor is that when it’s cold outside, it can struggle to reach the operating temperatures for proper combustion. It’s for this reason that you don’t need a choke if you’ve got a fuel-injected bike since fuel-injected bikes are much more tolerant towards cold temperatures. If you’d like to know more about the differences between carburetors and fuel injection, check out episode 29 of 30 Minute Motorcycling. Anyway, because carburetors struggle to reach operating temperatures in the cold or when the bike’s been idle for long periods of time, the choke is therefore used to give the carburetor a quick boost by temporarily injecting more fuel than air into the combustion chamber. So, how do you activate the choke? The short answer is, it depends – on your bike that is. Typically, the choke will be a switch or a button that you have to press or flick to activate the choke – but some chokes consist of a lever that you have to squeeze while you start the bike. When you activate it, a so-called “butterfly valve” activates and the amount of air that goes into the carburetor gets restricted or “choked” – hence the name. No matter what type of choke you’ve got, it’s important that you deactivate it as soon as your motorcycle, moped, or scooter’s up and running. Some chokes deactivate automatically when you roll on the throttle, but most of them need to be deactivated by hand. But why do you need to deactivate the choke once your bike is running? Because remember – the choke increases the amount of fuel that ends up in your combustion chamber. Therefore, if you leave the choke on, it will continue to burn fuel for no reason. The bike’s already running fine – there’s no need for more fuel. In fact, you might notice that your bike will start to “run rich” if you leave the choke on. If you’d like to know more about “running rich” and some common symptoms of it, please check out episode 19 of 30 Minute Motorcycling. And that’s what the choke is, what it does, and how to use it. To summarize, the choke is used to get your carburetted motorcycle, moped, or scooter up to operating temperatures from a cold start by temporarily feeding the engine more fuel. The choke itself is either switch, button, or lever that when activated, restricts the amount of air that enters the carburetor, thereby, making the mixture richer with fuel. Once your bike is running, remember to turn the choke off, to avoid burning too much excessive fuel. And finally, only carbureted motorcycles, mopeds, and scooters have chokes – fuel-injected bikes are more resistant towards low temperatures and therefore don’t need chokes. For more information about the choke, I’ve put a few links in the show notes to a blog post on The Dual Wheel Journey about it, as well as to a video from the Tomos America YouTube channel that explains the choke brilliantly. Until next time, keep your helmet on, and your eyes on the road. Bye!