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In the context of motorcycles, and other two-wheelers that run on petrol or gasoline, “running rich” isn’t a good thing. 

Tune in to discover:

  • The concept of “Lambda 1” – and what “running rich” really means
  • 4 reasons why “running rich” isn’t good for your bike


Hello and welcome to 30-minute motorcycling – a podcast for new aspiring and returning riders where you’ll learn about motorcycles and other two-wheelers in 30 Minutes or less. 


“Running rich” might sound like a good thing, but in the context of motorcycles, and other two-wheelers, “running rich” takes on a different meaning. 


And in this episode, you’re going to learn why “running rich” means, and 4 reasons why it’s not a good thing.


First, though, we need to talk about a concept called “Lambda 1.”


In the context of internal combustion, Lamda 1 represents the most ideal mixture of fuel and air that enters the combustion chamber. 


There’s some complicated math to this formula, but in layman’s terms, the more even the fuel/air mixture is, the closer the value will be to Lambda 1. 


If the value is below Lambda 1, it means that the mixture contains more air than fuel, which is known as “running lean.”


On the flip side, if the mixture contains more fuel than air, the value will be above Lambda one which results in “running rich.”


So essentially, that’s what “running rich” is. But why is that bad? 


First of all, if your engine’s running rich, there’s be an awful rotten-egg like smell coming from the exhaust. Since there’s more fuel going into the combustion chamber, there’s more carbon build-up, which in turn means stronger emissions.


But a foul smell is just the beginning – your engine’s performance will suffer too. 


Remember that in an internal combustion engine, the power is delivered through a mixture of fuel, air, compression, and an electrical spark.


If the air is removed or reduced from the equation, the combustion process is incomplete and therefore less effective. 


But engine performance isn’t the only thing that will worsen – your fuel economy or gas mileage is also affected if you’re running rich. 


Since there’s more fuel in your mixture than your bike needs, you’ll burn through more fuel – all your bike’s performance is massively reduced. Quite a waste, isn’t it? 


Not only that, but if there’s more fuel in the fuel/air mixture, it means that your spark plugs will be clogged up with carbon fouling.


And there’s an easy way you can tell – simply remove your spark plugs and check the central and ground electrodes – i.e. the bottom part of the sparkplug that goes inside the engine. 


Do these electrodes look like they’ve been dipped in tar? Then, that’s a result of carbon fouling – which in turn is a result of a rich fuel mixture. 


So why is carbon fouling a problem for a spark plug? 


If you’ve listened to the 30 Minute Motorcycling Podcast episode about internal combustion engines, you’ll know that the job of the spark plug is to ignite the compressed fuel and air mixture during the “ignition stroke.” 


Of course, that’s assuming that the spark plug is clean. If on the other hand it is clogged up with carbon build-up, the ignition might not happen, which can cause everything from poor acceleration to the engine having difficulty starting. 


By now, you should know what “running rich” means and why it’s bad. Come to think of it, how many times have I said the phrase “running rich” in this episode?


Anyway, if you’d like to know about how you can solve a running rich problem, I’ve put a link in the show notes to a blog post on The Dual Wheel Journey about this topic. 


Until next time, keep your helmet on and your eyes on the road. Bye!