Several good things mentioned in this post:
1. Pick a target temp, but don't get stuck on it. My WSM loves to run around 275*. Anywhere +/- 25* of that and I am happy. If it is running lower than my target, I expect it to take a little longer. Higher, a little faster.
2. Start with less coals. Easier to increase temp than it is to decrease it.
3. Catch the temp on it's way up. When I hit 250*, I usually close two bottom vents, give it 15 mins and see where it's at.
4. Weather can be a factor. Make sure your open vent doesn't face the wind. On hot days (100*), it might want to run a little hotter.
Blackened food can also be caused by putting the food on too quick and not waiting to get Thin Blue Smoke (TBS). You should barely see any smoke coming out of the top when you throw the meat on. Takes my WSM about 20 or 30 mins to get to that point. White, billowy smoke is not good eats.
It takes me less then 4 hours to make spares at around 275*. I usually do 2 hours nekkid, 30 - 45 mins foiled, and then the rest of the time nekkid again. When I take it out of foil, I pick up a rack from the end with a pair of tongs. They are done if they bend to nearly 90*.
Good luck. It took me several times and a lot of reading to get it right...