I recently installed a Zex nitrous kit on my 98 Cobra and so far I have run 2 bottles through it. The first bottle was used up mostly on my purge kit install and a few test runs. I took the car to the track and right before I staged for my first run I purged. All I got was a tiny little white puff and then only clear gas. I thought I had run out of nitrous. The next day I took the bottle out and weighed it. I still had like 3 lbs. left according to the scale. (The bottle weighs 14.1 lbs. empty and it weighed 17.1 lbs.) I let a little spray out and it was warm and clear - not freezing cold and white like nitrous oxide is. I emptied the bottle into the air and then got it refilled. I figured the stuff in the bottle was skunked and I didn't want to top it off and ruin all the new nitrous. I took this bottle to the track and got instant results. I got a 12.56, a 12.71 and a few 12.80's. I was content. I then took a few weeks off and then took the car back to the track. AGAIN...right before staging on my FIRST RUN, I purged and got a little white puff and then CLEAR SPRAY!!! I took the bottle out and weighed it when I got home and had about 3 lbs. left AGAIN!!! Why is the last 3 lbs. of nitrous turning to crap??? I realize when the bottle gets near empty you can start to feel "surging." I felt NOTHING! Am I doing something wrong??? I closed the bottle after every use and purged out also. Should I be taking the bottle out of the car??? Am I not doing something that I should be???