I have a 2002 Harley fat boy that is stock except for a set of Vance and Hines short shots. I have installed a CVO Performance idle mixture screw that I have set at 3 turns out. Is this the right setting for the mixture screw? Is it lean or rich

 

No one can answer that question with certainty... That's not how a carb bike is tuned...

Someone with similar mods can give you a starting point, but each bike should then be tuned using it's own reaction to changes made to the carb.

On a bike like yours, with just an exhaust... it should run well very close to the stock set-up of the carb. You should not need to get an aftermarket ICM to adjust timing with just exhaust or exhaust & air cleaner mods. If you go with bolt-in cams, or a big bore kit, you will need to invest in another ICM that allows timing curve changes, along with tuning the carb.. to get the performance out of your mods...

Start with the OEM pilot & main jets, along with the OEM needle... You will probably get by with just tweaking the mixture screw.

If you have (or add) a high flow air filter too, you might need to change the needle or a jet.... but probably not...

In any case, you start with the OEM carb. Then as you tune it, the way the bike runs, will let you know what you should do...

There are instructions and guides on this web site that will tell you how to tune your bike...

https://cv-performance.com/instructions-guides

The Vance & Hines Short Shots are..... well.... short...

As such they reduce back pressure and will cause you to lose low-end torque. There are things you can do to minimize the amount of low-end torque loss, but you will need to tune it first, see if you like the way it runs, then decide if you want add something like lollipops to add back pressure to regain some low rpm torque loss, then you will need to retune for them...

Just to give you a comparison for your tune...

I have a 2001 FXSTS Springer softail with Vance & Hines Straight Shots exhaust and a high Flow Screamin' Eagle air cleaner. The rest of the engine components, including the ICM, are OEM. After a complete carb disassembly, cleaning (ultrasonic cleaning tank), rebuild of all wear parts, and setting the float, I tuned it on the bike. I used the OEM 45 pilot jet, 190 main jet, and a CVP Velocity needle. It took almost exactly 2 turns of the mixture screw and the bike runs excellent, starts easily, and averages 41 mpg.