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techtalk:evo:carb02 [2020/01/12 20:02]
ixl2relax [The Idle/Transfer Ports Operation & Tuning]
techtalk:evo:carb02 [2020/01/12 20:04] (current)
ixl2relax [The Idle/Transfer Ports Operation & Tuning]
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 **Main Jet** - The Main Jet itself does not begin to limit fuel delivery to the carb operation until the vacuum slide is 75-90% wide open and the engine is revving. Until then, other parts & factors (such as the idle mixture screw, slow-jet and needle position in the needle jet) are controlling the fuel utilized by the carb. **Main Jet** - The Main Jet itself does not begin to limit fuel delivery to the carb operation until the vacuum slide is 75-90% wide open and the engine is revving. Until then, other parts & factors (such as the idle mixture screw, slow-jet and needle position in the needle jet) are controlling the fuel utilized by the carb.
  
-**Needle & Needle Jet** - The needle is a tapered, nail-like, rod that operates from the bottom of the slide into the needle jet. It does not affect the flow of fuel until the throttle plate opens sufficiently to create an active vacuum in the outer section of the venturi, which will lift the slide and move the needle in the needle jet. The fuel mix supplied thru the needle jet, by your selected needle and the emulsion tube, will combine with the transfer fuel mix of the slow jet as the carb operation moves out of the transfer period into the mid-range of the throttle/​slide function.\\ The main jet, located at the bottom of the emulsion tube, is way below where the needle rides and has no relationship with what the needle does other than to create an eventual upper fuel limit at WOT. ((wedge of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1820463&​page=9)) The needle rides in the needle jet which is the silver jet (hollow cylinder) that sticks up from the bottom of the throat of the carb and the needle moves up and down thru it during operation.\\ The tapered needle and needle jet together control fuel flow coming out of the emulsion tube into the throat. After the needle is almost up and out of the needle jet, then the main jet will become the limiting factor for the fuel flow at the wide open throttle position (WOT). Until the needle gets out of the way, the main jet is doing nothing to limit the needed fuel.\\ ( See this [[http://​xlforum.net/​forums/​showthread.php?​t=165259|XLForum Thread]] on needle dimensions)+**Needle & Needle Jet** - The needle is a tapered, nail-like, rod that operates from the bottom of the slide into the needle jet. It does not affect the flow of fuel until the throttle plate opens sufficiently to create an active vacuum in the outer section of the venturi, which will lift the slide and move the needle in the needle jet. The fuel mix supplied thru the needle jet, by your selected needle and the emulsion tube, will combine with the transfer fuel mix of the slow jet as the carb operation moves out of the transfer period into the mid-range of the throttle/​slide function. 
 + 
 +The main jet, located at the bottom of the emulsion tube, is way below where the needle rides and has no relationship with what the needle does other than to create an eventual upper fuel limit at WOT. ((wedge of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1820463&​page=9)) The needle rides in the needle jet which is the silver jet (hollow cylinder) that sticks up from the bottom of the throat of the carb and the needle moves up and down thru it during operation. 
 + 
 +The tapered needle and needle jet together control fuel flow coming out of the emulsion tube into the throat. After the needle is almost up and out of the needle jet, then the main jet will become the limiting factor for the fuel flow at the wide open throttle position (WOT). Until the needle gets out of the way, the main jet is doing nothing to limit the needed fuel. 
 + 
 +( See this [[http://​xlforum.net/​forums/​showthread.php?​t=165259|XLForum Thread]] on needle dimensions)
  
 **Emulsion Tubes** ((stevo of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=2876)):​ - As the throttle plate is opened further the main circuit comes into play. Fuel enters the bottom of the emulsion tube thru the main jet. Air enters thru the main air bleed jet in the front of the carb. The air and fuel are mixed into an emulsion in the emulsion tube before it passes up the tube past the needle jet and needle into the carb venturi and down the intake chasing after (combining with) the idle circuit fuel. The size, number and position of the holes in the emulsion tube effect the fuel delivery. More holes = more air = leaner mixture. More holes at the top = leaner mixture at low speeds. More holes at the bottom = leaner mixture at high speeds. If you change emulsion tubes you need to use a compatible needle. It will also have an effect on the main jet size (at WOT) and quite often the pilot circuit thru the just-off-idle response. Needles, needle jet, emulsion tube (size, position and amount of holes), main air bleed size and main jet are all closely linked. Changing one can affect the others and all have an affect on the fuel delivery to differing amount at different throttle positions. **Emulsion Tubes** ((stevo of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=2876)):​ - As the throttle plate is opened further the main circuit comes into play. Fuel enters the bottom of the emulsion tube thru the main jet. Air enters thru the main air bleed jet in the front of the carb. The air and fuel are mixed into an emulsion in the emulsion tube before it passes up the tube past the needle jet and needle into the carb venturi and down the intake chasing after (combining with) the idle circuit fuel. The size, number and position of the holes in the emulsion tube effect the fuel delivery. More holes = more air = leaner mixture. More holes at the top = leaner mixture at low speeds. More holes at the bottom = leaner mixture at high speeds. If you change emulsion tubes you need to use a compatible needle. It will also have an effect on the main jet size (at WOT) and quite often the pilot circuit thru the just-off-idle response. Needles, needle jet, emulsion tube (size, position and amount of holes), main air bleed size and main jet are all closely linked. Changing one can affect the others and all have an affect on the fuel delivery to differing amount at different throttle positions.