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Does the air screw affect the main circuit?

  • Thread starter Thread starter pasteurized
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pasteurized

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I am thinking no... the air screw and the fuel pilot screws are used solely for the idle/pilot circuit, right? I finally got the idle circuit pretty close to dialed in and synched but now the main circuit is running out of gas when I wring it out. Before getting the idle circuit set up, the main circuit was PERFECT (using jetting specified by Vance and Hines, stock airbox), and the machine screamed to redline and pulled like hell all the way. Now that I got the idle circuit set today it doesn't want to pull in the higher rpms. What gives? I don't believe I have any air leaks... it has to be something directly relating to carb setup.
 
In your VM carbs, the air jet and its passage (regulated by the side air screw) also connect to the needle jet/bleed pipe. This allows good atomization of the fuel as it enters the carb throat. All 3 jetting circuits are effected.
Setting up the pilot circuit correctly should not cause a high speed or main circuit problem. I don't know what you have done to the pilot circuit to create a wide open throttle problem. If you adjusted the side air screws too far in, rich, this could cause a problem though. Too far out can cause decel' popping, etc.
Where are they set? Where are the pilot fuel screws (underneath)set at? What does the bike idle at when warmed up?
 
The pilot fuel screws are set to roughly 1.5 turns out, and the air screws are around 2 (each are a little differently set). I have synched the carbs and the bike idles at 1100-1200 when warmed up. It just suddenly feels like it needs much bigger main jets after tweaking the pilot circuit, and I am dumbfounded as to why.
 
If the airbox is stock and still has its lid on, 1 1/2 turns out on the pilot fuel screws seems too much for just a pipe. 1 full turn seems better. The side air screws should be set using the highest rpm method, but 2 turns out is "ballpark."
These settings would not cause a problem with the main circuit.
You have me confused as to how making some pilot circuit adjustments has caused a main jet problem or fuel starvation/lean problem? Something else is involved here. Can you let us know everything you've done to the bike? What's the bike doing that you think it's starving for fuel now?
 
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