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Pilot vs. Idle mixture screw

  • Thread starter Thread starter redruM69
  • Start date Start date
R

redruM69

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I asked this question on the end of an older thread, but its pretty much buried so I'll start a new thread.


On the CV Carbs, what differences do the idle mixture screw vs. the pilot jet have on low end/slight throttle? Does one affect mixture more in a different range than the other? Or are they the exact same circuit, and one just compensates for the other?


Thanks!
 
The screw provides a range of fine adjustment in the pilot circuit. Once it reaches the limits of it's adjustment you then need to look at pilot jets or pilot air jets.

Dan :)
 
Air enters the pilot air jet and pulls gas from the main jet. Since the needle is blocking the main jet it is diverted through the pilot jet and premixed with air from the pilot air jet. It is then regulated with the idle mixture screw. All the circuits affect the others. If you are rich with the pilot circuit the needle circuit will start rich and tuning you will have to compensate for it. The same applys for the needle circuit to the main jet circuit.
Ideally you want all the circuits to be right so you pass through all circuits with no hesitation or hiccups.
 
the pilot fuel jet and the idle mixture screw are a part of the same circuit (that also includes a pilot air jet)

1. the pilot fuel jet dictates the maximum amout of fuel in the pilot circuit

2. the idle screw moderates the amount of the air-fuel mixture (that mixture due to the combination of the function of the pilot fuel jet and pilot air jet) that is discharged into the cylinders


A. when the throttle is closed the amount of the pilot mixture released into the cylinders is controled ONLY by the pilot mixture screw

B. when the throttle is very slightly opened, part of the pilot mixture by-passes the mixture screw and is discharged into the main venturi tube directly where it mixes with the main airflow

---

the idle mixture screw gives you a finer and easier adjustment of the pilot circuit than if you had to change the pilot air and/or fuel jets
e.g. - on 2.5 turns out on the mixture screws my bike backfires a lot on deceleration, but at 3.5 turns out it doesnt backfire at all
 
Last edited:
Chef and psyguy beat me to it, all I was going to say was that the pilot fuel jet and the pilot air jet set the ratio for the pilot mixture. The adjustment screw only regulates how much of that mixture gets into the main air stream.

.
 
Steve said:
Chef and psyguy beat me to it
Click to expand...
heh, steve, i can relate to that...
because of the time difference (between here and most other places on earth) and so many responses sometimes only minutes after the first post i often find it redundant to add anything else
what a great forum!
 
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