Discussion in 'Norton Commando Motorcycles (Classic)' started by Tornado, Jun 28, 2018.
Correct term is actually to ENRICH the startup mixture. Hence the term "enrichers".
Totally different from the original concentrics.
A fair correction.
I've removed the chokes on my 71 Commando. Tickle the carbs; starts on 1st kick. 99% of the time.
Tornado, the reason an enrichment device or choke is used to start a cold engine is that the engine needs a specific mixture of fuel and air (within a range) for the combustion process. Air is much lighter than fuel and fuel droplets will adhere to cold engine surfaces like intake manifolds etc. We therefore need to oversupply fuel at cold start to get the process going, once the engine warms up the fuel no longer sticks to the hotter components and if the carb is correctly set up it should not require tickling for subsequent starts. The choke on an Amal moves the point of suction rearward in the throat of the carb allowing some fuel to be drawn through the main jet for starting and also slightly restricts the amount of air drawn in and therefore richens the mixture.
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