Why does this keep happening? (Tube question)

[Denial]

So, I've been working with tube for about a month now, mainly implosion marbles and some random pipe action.. This question is pertaining to my marbles and other closed solid masses made with tube. I am constantly getting this little, or sometimes larger, bubble in the solid mass. It looks like the tube isn't fully closed while working it in the flame, it looks like an air line basically when you start to close a tube and you have that tiny line going through the glass you know to keep working it and close it up more until that goes away.. This is like a larger version of that, problem is I keep working it and working it, mainly keeping the tube straight with the table, not using elbow down or up its just straight with the table, then ill try elbow down like you would to gather glass and go back to the first one. Sometimes it gets smaller, sometimes it doesn't. My mainly problem is I can never get it to go away completely and it's taking a lot longer to get it to close up or go away then I think it should.. Something just isn't right.. So my question is, what the hell is this, I know its a bubble, but how do I get it to go away, or remove it from the mass? I've even tried tearing glass off the top before closing the top and melting it into a sphere, this leaves me with a smaller bubble sometimes but it also takes a lot away from the size of the marble and pulls the art..
If anyone can help me out in the least, I'd be very thankful, I don't know why I'm having such a problem with such a simple thing.
Here are a couple pictures on a little implosion I did quick just to show what I mean.
4258442585

[ALIEN!]

keep heating it from the front and side, trying to keep flame splash on the blowtube minimal, this is a good trial in keeping a proper heat base. Basically you are trying to get all the air out before the blowtube collapses in trapping air.

Easiest way to do this is by using twice the length of tubing you are using now. Try using a 2 inch chunk of 25 mm, 1 inch on the handle side will be trashed, but having that there will make it a ton easier to close up all the colored area w/o air trap.

[ALIEN!]

I also suggest rod for implosions that end up round and tube for implosions for discs or flat/wide pendants.

[Denial]

Thank you for your fast reply, damn..
I am using 25mm right now, I thought I was already using a pretty decent size point, and blowing my bubble fairly medium size.. Are you saying to pull an even larger point to work with or blow an even bigger bubble? Or whatever size bubble, then blow out more glass once I get back to the end of the point once the bubble has condenced? Pretty sure what you're saying is I should be focusing my flame just at the from more and go slower?
Am I correct in keeping the tube at a slightly downward angle towards the torch during the condencing process or should it be more angled with the table? I'm confused on this because I keep hearing different things from different people, figured I'd just ask you.
Thank you again for your quick response.

[Zed]

Are you using cut rate tubing? Some of the china and other cheap-o tubing has a cord in it that will form a air bubble in your work. Try some simax and see if the problem persists.