I'm havin trouble with my first infusion where iv got a tiny air leak sumwhere and I can't find it.

In my experience the cause of the leak was ALWAYS the same! It was the infusion mesh flow media!
Any where you have a cut edge in the bag of the flow media is sharp. If you picture it as the sharp edge of a chain link fence you can imagine how easily it will puncture the bag. To solve this problem I simple cut strips of peel ply ( just 2 inches wide) and place them over EVERY single cut line of the flow media! I have NEVER had a leak since and I do a lot of infusion. Before I did this technic I NEVER had a perfectly sealed bag, and I thought it was impossible to have one.
Try it and you will become a believer.
Hope this helps.
Fred