Going only by the information that you have provided, I think two holes are too many for that consistancy of e-liquid; a single hole would likely eliminate the symptoms you setup is having. You may also be puffing too hard....slow, long 5 second drags work best.
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Flooded carto's in a tank seems to be the most common complaint for beginners when they try a carto tank. The second most common is just the opposite - dry hits or a burnt taste.
There's a common learning curve in setting up a cartotank and a fine line of getting the proper amount of e-liquid into the cartomizer. These tanks work on the principle of negative pressure within the tank enclosure. Sucking on the drip tip causes negative pressure within the tank, drawing more liquid into the cartomizer. The liquid from the tank that goes into the carto is replaced by air; hense the air bubble that you can observe coming out of the cartomizer's hole after taking a pull from the carto.
Flooding can be caused by a number of factors; most of them user related. There is always the possibility of just getting some bad cartomizers or a leaky tank, but I tend to think this is not the norm.
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Improper technique of filling the carto before it is introduced into an assembled tank is one factor. No e-liquid should be allowed to enter the center air hole in the top of the carto when drip filling. I eliminate this issue by
plugging the hole with a wooden tooth pick. The carto should have e-liquid applied until the polyfill is moist in appearance like a slushy drink.
The carto at that point is ready to be inserted about
half way into the
assembled tank, through the
bottom end cap. Drop your e-liquid through the space between the top cap and the cartomizer, again taking care to not get liquid into the top of the carto. A tank accessory or filling tool is useful for this purpose.
Fill the tank approximately
80% full. Then push the carto up through the top endcap. Remove the tank tool if you use one, and then put a drip tip on the carto. Some people do a primer pull (puff without power) to ensure the carto is wet. I tend to do a test vape first. My feeling is if you have already primed the carto properly beforehand, the primer puff is unneccesary.
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Putting the carto all the way into the bottom cap and filling the tank before placing the top cap on will disrupt the pressure in the tank causing too much liquid in the carto - leading to flooding.
I think some people use an improper method of puffing on cartotanks. I use a
slow, steady 5-second puff. This allows the proper amount of juice to enter into the carto from the tank. Too hard of a puff can cause too much liquid to enter - leading to flooding.
Too many or too large of a hole in the carto can allow too much liquid into the carto. I have had great success with a single laser-drilled hole with a 50/50 pg/vg mix. More than 50% vg might require two holes. It often depends upon the individual juice and your individual vaping technique. If you are experiencing flooding with two holes, try a carto with just one hole.
Punching your own cartos can lead to issues.
Punching too deeply can damage the internal air hole, causing irrepairable damage to the carto. Using a tool to punch holes invariably causes some distortion to the carto tube, causing it to become oval instead of round at that point. The distortion can make passage of the carto through the end caps difficult and cause unnecessary wear and tear on the inner o-rings.
Damaged o-rings can cause air or liquid leaks in the tank or carto leading to flooding.
To see a demo/review of the recommend Slap-Yo-Momma tank tool, watch this video:
A PBusardo Review - Slap Yo Mama Multi-Purpose Adapter - Big Daddy Vapor - YouTube
I recommend viewing the following demo video on priming the carto, intalling it into the tank, and filling/refilling a tank.
I punched all five I have caused the first test one seemed fine initially. .... have a new shipment of cartos coming. 
