Any time a change is made to the air intake/flow, fuel delivery, and or exhaust rejetting and carb tuning may be in order, usually these are changed with aftermarket or modified exhaust and intake. The exhuast may only require a simple fuel mixture screw adjustment on the carb, but an aftermarket intake or a modified stock intake requires more fuel to match the increased airflow which can only be corrected with a carb rejet.
Pulling the carb(s) apart for a rejet, cleaning, or rebuild is something that gets easier the more you do it, and may seem scary or difficult at first but is a necessary task for keeping your VLX tuned properly and sometimes running right. Below are a few pictures for reference to help you when working with the particular carburetor setup on your VLX.
Courtesy of VT750DC.com: All CV carbs follow the same theory to operate. There is a pilot jet, a main jet, a needle, a slide, and a mixture screw. See the picture below to understand the parts and components of all CV Carbs including how fuel is delivered at idle versus at throttle.
Based on throttle position fuel id delivered from different circuits within the carb. See the Chart Below for reference to see how each throttle position leads to fuel delivery overlap.
Also see the Jet Needle diagram which explains the needle clip position effect on fuel delivery, as well as the position of the needle at various throttle positions:
For help tuning your motorcycle please see the Plug Chop Tuning Method Forum Thread at Shadowriders.net
For help removing dual carbs from your VLX and rejetting see the Shadowriders.net Kajima Velocity Install & Stock Airbox Removal.
Below are exploded diagrams of both the older dual carburetors and the newer single carburetor included for reference pulled from the factory parts microfiche. This will help you understand the parts of your carburetors.
If you have a dual carburetor model VLX pulling the carbs is a little bit more difficult and requires a little finesse as it is a tight fit with limited space to operate in between the frame and the engine where the carbs sit.
Diagram of the dual carb setup of the DC Spirt and ACE (right click images and choose to open in a new tab or window to see a larger version) for reference:
If you have a single carb setup model VLX pulling the carb is a fairly easy task requiring you to meerly disassemble and remove the intake, then disconnect the vacuum hoses and fuel line, and finally loosening the clams so you can remove the carb.
Carburetor Diagram (right click images and choose to open in a new tab or window to see a larger version) for reference: