What temp were you trying for, and how were you measuring that temperature? Were you adding more fuel to raise the temperature, or to keep it from dropping as fuel burned out? How long did you give it to let the temp come up? Did you have water in the water pan? How long did you cook the ribs?
I use lump, and here's my process, assuming you want a low-and-slow cook with a temperature in the 225-275 range. I don't use water in the water pan. I've got an 18", so your vent settings may be a bit different, but the concept should work just fine.
Fill up the charcoal ring most of the way with un-lit lump. Mix in wood chunks for smoke.
Use a chimney starter to get about two handfuls of lump lit. Once they're lit good, dump them on top of your pile of un-lit coals in the charcoal ring, and spread them out a little.
Add a wood chunk or two right on top of the burning pieces.
Add more un-lit lump on top (if doing a really long cook like a pork butt or brisket, not really needed for ribs, which should only take about 6hrs at low temp and won't use a ton of fuel)
To settle the temperature in around 230*F give or take a bit, I open the top vent about 1/8 inch, keep two of the bottom vents shut completely, and open one bottom vent about 1/8 of an inch.
Doing this, it takes about 45mins or so to hit that 230*F temp. But by letting the temperature come up slowly I can make sure I don't overshoot it, because if you go too hot it takes it a while to bring the temperature back down, especially if it's hot outside (which it always is here in middle GA).
I cooked ribs this weekend, using the above procedure. It held right at 230-240 almost the entire cook without any adjustments. The smoker temp did go up a little as the ambient temperature outside rose in the afternoon, the smoker got up to 250*F, and when it did I tapped the bottom vent closed just a smidge and the temp dropped back down to that 230-240 range the rest of the afternoon.
Things to keep in mind:
Nothing happens fast with a smoker. When you adjust the vents, give it time to see the change take place. Could take half an hour or longer.
Low and slow needs a really small fire, especially if it's hot outside (it was upper 80's / low 90's this weekend for my cook), so don't start with a lot of lit coals. And it doesn't need much air to maintain that small fire, which is why I don't open my vents much.
When you open the lid to add meat, or check on it, you're giving the fire a big gulp of fresh air, the temperature will go up a bit, but just leave your vents alone and it'll settle back down in a few minutes.
If you're wanting to cook hot and fast, open the vents up and light more coals with the chimney starter. Mine will run at 400*F with lump with all the vents open.
EDIT to add, one last note: Fill that charcoal ring up! There's no problem with starting with more fuel than you need, when you're done cooking just close the vents and the fire will go out, and you'll still have a lot of fuel left over you can use on your next cook. It's just like driving a car: more fuel in the gas tank doesn't mean the car goes faster (aka smoker runs hotter), it just means you can drive further (longer burn time) before you run out of gas.