I got a C02 inflator and decided to learn how to use it rather than get a bad surprise on the road. To simulate a tube change:
1. I deflated my front tire.
2. Put a touch of air in using the C02 inflator, to simulate verifying the tube was not pinched.
3. Filled with inflator and checked pressure with a gauge. It read 180 psi. This was from a 16 gram cartridge.
4. Deflated the tire.
5. Re inflated the tire using a floor pump.

Next day tire is flat. What am I doing wrong?

Thanks!

Possibly the tube failed at the valve stem base due to too much harsh manupulation. Remove the tire and check where the failure occured. BTW, a 16 gm CO2 is too much for a 700x23 typical road tire and 180 psi is well beyond the max pressure recommendation.

You did everything right. Your gauge is somehow wrong (either defective, bad reading, etc.) because a 16g cartridge won't supply that much to a 23/25 tire and a tire won't stay on the rim with that much pressure.

You've got it down so I would just ride now knowing you can fix a flat comfortably.

As far as the next day flat, you probably had the tube caught under the rim

Remove the tube and locate the leak.

Also a 16g cartridge inflates a 23 tire to 130 lbs and a 25 tire to 120 lbs. That's the absolute max and assumes 100% of the air goes in. That's very rare because you usually get some leakage. But if you don't, back off and don't quite put all of the inflation is.

my bad the gauge read 80 not 180. I'll take it apart and find where it failed.

Tires filled from CO2 will deflate quickly, they are great for on the road, but I always re-fill up when I get home with normal air. here's an old post about this issue https://www.bikeforums.net/archive/in.../t-154847.html

I assume you are saying you deflated the tire and refilled it with air from your floor pump and it was flat then you do most likely have a hole someplace.
But if most of the air was from the Co2 it will deflate over night CO2 air will leak out from the tube you should always after using a CO2 when you get a chance remove all CO2 gas and reinflate with air from a floor pump or compressor.

In my opinion that's the biggest drawback to using CO2 - the lack of a second chance.

When I inflate a tire using CO2, the first thing that I do is to blow into the inner tube to give it shape, install the tube in the tire, and finally install the tire onto the rim. Then I check both beads all the way around to be sure the tube isn't caught under the tire bead anywhere. Only then do I use the CO2 to inflate the tire.

Checking both tire beads all the way around can be an enormous time saver.

That's why I carry a mini-pump and CO2. The mini-pump is used to put 20 psi or so into the tube to be sure it is good and seated properly. Then the CO2 is safe to finish bringing the pressure all the way up.

I don't bother with CO2 because it's a constant expense and remember to buy more when I run low, I have limited air supply, I have empty carts to hassle with, and then have to drain the air out and refill when I get home. I can't be bothered.

80psi does sound more like it. You want to look at the tube to find out why it failed, if at the stem base then you put too much side to side pressure on the valve at one of the times you filled it up and tore it.

If the actual valve is leaking you may have over tightened the little valve nut on top, or maybe forgot to close it. You only have to close the valve nut just tight enough where the nut simply feels friction just beginning and no more. Maybe you bent the little rod at the end of that small nut from putting too much pressure on the valve during pumping. These valves are fragile and don't last forever so you need to be careful with them.

Or maybe you have a tiny leak from something penetrating the tire or a spoke poked through a worn out rim strip.

"I don't bother with CO2 because it's a constant expense and remember to buy more when I run low, I have limited air supply, I have empty carts to hassle with, and then have to drain the air out and refill when I get home. I can't be bothered."

Me neither. I have a Topeak Road Morph G. Air is free and unlimited. Pumping is a good cardio workout. I can help other riders and not worry about leaving myself short.

Of the flats I've experiences over three years and 7000 miles, two were failures at the valve stem. I spent some time pondering this problem including questioning the local bike shop. What I discovered after much pondering and probing was that the rim itself, after boring out the aluminum at the plant, was left with a sharp and somewhat ragged edge at the valve hole. This is known as a manufacturing flaw. My solution was to peel back the rim tape a few inches and chamfer the valve hole with a tiny rat-tail file and 150 grit sand paper. This alone should have resolved the problem but in addition I also cut out a small piece of rubber from an old tube, about 25 x 25 mm, with a very small hole and pressed it on over the valve for extra protection of the tube. So far, in the last 2000 to 3000 miles, no flats of any sort.

As extra, extra precaution, I also inspect the tires every 7 to 10 days or so and pick, out of a deflated tire, any glass or debris I find embedded in the rubber. I frequently find potentially flat producing junk in the tires which is not surprising as there is all sorts of trash on our roads.

12 gm, unthreaded CO2 cartridges are cheap and available at any sporting good store or the sporting goods department of any X-mart. I buy them in boxes of 25 for less than $15. The main benefit of CO2 for road-side flat repair is speed and much less chance of damaging the tube's valve. Yes, you have to replace the CO2 with air after you get home but it's a lot easier with a floor pump than a mini-pump.

Not such a big deal, I generally top up my tires before every ride anyway so replacing the CO2 takes care of itself.

I used to use CO2 with my road bikes because it's so much faster and more convenient but my recumbent tires have a lot more volume so even a 16 gram cartridge doesn't cut it. I'm back to using a pump.

I carry both pump and C02 because even with bug dope on mosquitos are a real pain at times, locally, which shows how everyone has different needs. I use the pump to find the hole and double check that there isn't a second unseen hole after I do a patch. Then I use the C02 to get me up and out as quickly as possible. It's just a convenience thing but it came in very, very handy once when I developed a slow leak while it was raining. I'd go a few miles, top off with C02 and keep riding. Much better than stopping to fix a flat in the rain or get the pump out each time.

I have several pumps, I don't have to waste gas going to any sporting good store and then waste money on CO2 because I get my air for free.

Speed? What the heck for? Are you racing every day? If I was racing without sag support then I would use CO2, but I'm not racing. It probably takes me about 1 to 2 minutes to pump air into a tire depending on the pump I use, I don't find that objectionably slow.

Easier? wait, let me get this straight, you ride a bike, that's a lot more physical exertion then using a pump, but your concerned over the physical exertion of using a pump?...that's just weird. If your arm strength is too weak to pump air into a skinny tire then you need to consider a different sport because arm strength is important to riding a bike.

Sometimes, if you are riding as part of a group, it is faster to use CO2, so as to get back on the road as quickly as possible. It is called being considerate of your ride partners.

Bike riders love to critique other bike rider's choices. Check out rekmeyata's and Jed 19's posts for example. If you use CO2 you don't have to put up with it for as long a period as you do if you're using a pump.

You got me on that one.

Most riders I know don't ride in groups, I have a few friends I do ride with but rarely do due to time constraints for all of us, we all use pumps, so we don't care if we have to wait around gives us some time to talk. Besides most riders, even in groups can't fix a flat as fast as I can, so usually I have to wait a lot longer for the flat to be fixed then airing up process. I'm not one of those impatient riders that need everything to be done right now or I'm going to raise a hissy fit, I think Americans are in too much of a rush and are extremely impatient and getting more so as time goes on. So it would do us good to wait a bit for a friend.

Heck I stop to help strangers on the road/path with bike problems (sometimes car problems!) and have to hang out for 45 minutes or so while I teach them how to fix a flat!! And they comment that several riders will past them and not one would offer to help. Why is that? We're too much in a rush, don't want to take the time out of our precious riding, it might ruin our training.

There are quite a few riders today that can't even fix a flat, they have a seat bag...with nothing but a cell phone it, and they use it to call their mommies who will come and pick up their little boy and take them to an LBS who will charge $15 or so to fix a flat.

Yeah, I know, I'm being rough.

And I don't care if someone wants to use CO2 that's their right, but for me it's a waste of money, resources, and time. I said for me.