Does clearing 2nd stage remove CO2/dead air?

I've read that failing to fully exhale inspired air while diving can lead to the build up of CO2 in a diver's air supply. Would clearing the second stage remove any/all build up of CO2? I'm asking because the last time I dove I felt faint and opted to surface prematurely. I am still in the process of determining if the cause of this feeling of faintness was due to the way in which I cleared my mask of water (I took a huge breath of air and forcefully blew it all out through my nose) or if my breathing pattern was causing a build up of CO2. I was breathing somewhat abnormally in order to become more or less buoyant at various times throughout the dive. My question is really a tangent of the self analysis I've been doing regarding my previous unsuccessful dive. Thanks for the feedback.

I imagine it's all in your head...no way C02 could build up that way. Besides, how else would you clear your mask?

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The 2nd stage has a low volume. Purging it will remove the CO2, but that's not relevant. And that CO2 is always there, independently of how deep one breathes.
Where you might have had a CO2 build-up was in your own respiratory system. If you were breathing shallow, trying not to cause buoyancy shifts, you may have been keeping some air inside your lungs and airways that wasn't being renewed. If you don't exhale properly, there won't be space for new air to come in, you'll just be moving used air up and down, with not enough fresh air replacing it.

Failing to fully exhale can lead to CO2 build up. The build up is between your lungs and your mouth. If you purge the second stage you are moving air from the tank, through the first stage, to the second stage and out into the water. It does not change the air space between your lungs and your mouth. So if you do have CO2 build up, purging the second stage isn't going to help.

Second, you don't need to forcefully blow air out your nose to clear your mask. In some cases, this wastes a lot of air and doesn't really clear all the water out of your mask. If there is too much force it will cause the water to splash around and not completely clear. You want to breath FULLY into your lungs then slowly BUT steadily blow out your nose to remove the air from the mask.

The best advice I can give you is "it is not a race." It is not a race to the bottom: take your time and keep track of your buddy. It is not a race to get suited up: you don't want to keep everyone waiting but racing to get ready will put you out of breath and a danger to yourself. It is not a race to get into the water. If your buddy is rushing you then you need a new buddy.

In the end, I would suspect you have over-exerting yourself and are not breathing deep enough. I hear people saying that when you breathing on a regulator it should be just like breathing normally. This is a not always good advice. If normal for you is breathing shallow but normally you aren't exerting yourself then you are fine above water. But once you are getting ready for the dive, you are wearing a lot more gear and exerting yourself. You will need to breath more deeply.

In general, you might want to look into breathing exercises. Even if you do breath well and deeply, getting better at breathing will help with your air consumption.

Also remember that scuba diving is not natural. Your body isn't used to this. After you have been diving for a while you will have built up the muscles and breathing to be a good diver. The most important thing is to relax and take your time until your body is used to doing this.

Dead space includes the tiny, tiny space in the second stage and mouthpiece along with the huge amount of space in your respiratory system that isn't purged when you breathe normally. If you are concerned about flushing the dead space as best you can, try this. Inhale deeply, then exhale all the way. Keep going.....exhale......exhale.....exhale.... until you think there is nothing left in your lungs. Now sing. Or say "Ahhhhhhh." You see, there was still plenty left. You can not get all the gas exchanged, but you can minimize it by breathing deeper on inhale and exhale.

As to your lightheaded feeling, that probably had nothing to do with CO2 retention. In fact if you hyperventilate and then valsalva strongly (like maybe clearing your mask too forcefully) you can pass out. Try relaxing. The sport is supposed to be fun.

It's not the regulator. Your restrained breathing to manage buoyancy is a much more likely culprit or being new an overall shallow breathing pattern. Aside from specific moments when you need to be spot on allow some porpoising.

Thanks everyone for the information. I'll def keep these things in mind when on my next dive.