I think this thing has something to do with injecting fluids in to the engine.

  • What exactly is an "idle" or "pilot jet"?
  • Does every car have one?
  • What is their functional purpose (i.e. what do they do)?
  • 2
    Please don't use a single comment on a forum as your question guide. It turns into a guessing game. You need to wrap something around the question like "In an automatic transmission there is an idler jet that I have heard of. It allegedly has something to do with the process of engaging a type of gear. Can someone provide additional information regarding this idle or idler jet?" Something along those lines. A breadcrumb or some type of artifact. Commented Jan 18, 2016 at 17:21
  • Thank you. I'll bear this in mind and try to improve my questions in the future. Commented Jan 18, 2016 at 17:26

1 Answer 1


An idle or pilot jet is a component of a carburetor.

It affects mixture at idle and just off idle.

The main jet affects mixture at off idle all the way to wide open and takes over mixture of the AFR at higher engine/intake tract airflow speeds.

The idle jet is often affected by air and fuel screws that can adjust the AFR during idle and closed throttle operations.

An incorrect idle AFR can result in backfiring under close throttle high RPM operations of an engine, especially under load and deceleration.

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