You do normally see some smoke, but that's not a good indicator of your tune. What you are looking for is at WOT to be able to pinch the fuel line and hear a distinct rise in rpm's. If someone has a tach you can use, 500 rpm is generally good. Most of the time, if you then raise the nose of your plane like you're doing a loop, the engine will rise on its own to that point, telling you that you have a perfect tune in the worst case scenario for fuel draw, which means you're a touch rich everywhere else. A very common mistake with a bad running engine is to start tweaking needles without knowing what your mix is now. You should be able to get a consistent rpm with any needle setting, and be able to see a consistent rise in rpm as you go leaner, then it peaks and stays the same for a few clicks, then starts to drop as you get too lean. When the high speed is properly set, then go to the low speed. If the engine idles and steadily drops rpm until it quits, you're too rich, If it idles a bit and rises in rpm before dying, you're too lean. The rich idle will change sound not long before dying as it loads up with fuel, but it will also die like that with a bad glow plug, too low an idle, or bad fuel. The difference is that the engine sound will stay the same as the rpm's drop and then stop. Get the idle right at a throttle setting that will run for a while, then lower your throttle and recheck. Don't go for the lowest possible idle, just low enough to where the plane won't pull itself sitting flat on the ground. Then check transition. Let it run for a full minute, then gun the throttle open. If it stumbles and blows a little fuel out of the exhaust, you're too rich. If it hesitates, you're too lean. With some engines, you have to make a compromise between good idle and good transition, but on most the right setting will give you both. The last thing to do is to check the high speed needle one more time to be sure it's still right. Air bleed carbs usually won't need any other tweaking, but some engines will and it's good practice to make sure before flying.

All of this assumes that your engine does not have any air leaks or fuel supply problems and isn't worn out. Generally, once you get an engine set right the only adjustments it will need after that is two or three clicks of the high speed needle to adjust for different atmospheric conditions. If you find yourself needing more than that, there is usually something wrong that has nothing to do with your needles.