Fuel screw location and description of operation.

These screws control fuel, and are generally known as "fuel screws". If you unscrew them, they will allow more fuel to pass into the carb at part throttle and make, primarily, idle mixture richer.
The fuel screws also, secondarily, affect part throttle / cruise - as in 2nd gear / 2,000 rpm, steady state operation - meaning that, if you think that you might need a larger pilot jet to correct a lean 2,000 rpm cruise, you could open up the fuel screws an extra amount (disregarding idle quality for the moment) and see if that helps the cruise.
Then, as long as you end up with best idle quality somewhere 1.5x to 3x turns out, you can enlarge the pilot jet size.

On most Mikuni carbs, the plugs are brass, have a very small hole in the center and about the diameter of a pencil. They may also be a machined disc of aluminum pressed into the carb body.

The VL1500 LC Intruder, like most Mikuni carbs of late, has the fuel screws located on the bottom of the carb, pointing up when the carb is installed. Often, you can see the tip of the tapered screw on the bottom of the bore of the carb, just "downwind" of the carb butterfly when the screw is turned all the way in.

Usually, if all jetting, including fuel level/float height,  is correct, the best setting for the fuel response and cruise operation will be in the range of 1.5x to 3.5x out from lightly bottomed out.
At less than 1.5x, try a smaller pilot jet and at over 3.5, try a 1 size larger pilot jet.
At more than 3.5x out, there isn't much spring pressure on the screw and it may fall out when in use.

The pilot jet and the fuel screws are the final control adjustment for idle and part throttle (like 1/8 throttle) operation.

The 2 brass fuel screw caps are circled in blue.

To remove the cap:

Get a self tapping screw, like a sheet metal screw and a drill bit that is equal to the "root" diameter of the threads.
Drill a small hole through the cap only. Be careful, the cap is only ~2mm thick and the head of the fuel screw is right below it - if you go through the cap, it's easy to ruin the head of the fuel screw!
After you drill the small hole, thread the tapered profile screw into the cap until it catches.
Gently lever the screw up and the plug will come out.

Marc Salvisberg

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