Sometimes the details and terms can be quite overwhelming for a brand new modelt/flyer. Your instructor is your best source to explain the terms in the above replies and for providing answers to your questions Since your instructor was present when the problems occurred, he/she is in the best position to find the cuase and correct the problem.

IMHO, N1EDM has already outlined very good points. I'll try to restate some for your understanding;

If, when the engine is running, you can see ANY air bubbles in the fuel tubing from the tank to the engine you have air in the line. This can be caused by loose fit of the fuel line on any connection -- at the engine, at the tank, or inside the tank. It could also be caused by a hole, even tiny pin ***** size, in the fuel tubing -- between the tank and the engine, or inside the tank. Replacing all the fuel tubing is often the least time consuming fix for these causes. I have seen cuts/holes in the fuel line on several RTF trainers, like the Alpha. Almost all were where the fuel line connects to the tube from the fuel tank. Perhaps they happen during manufacturer assembly or during shipping. One was at the engine connection, and may have caused by the trainee.

Another possible cause of bubbles in the fuel line is 'foaming' of the fuel in the tank, when the engine is running. This is stems from engine vibration shaking the tank and mixing air into tiny air bubbles in the fuel. The Alpha does not come with padding around the tank, and I have seen 'foaming' occur in about 10% of the Alpha trainers flying at our field in the past 18 months. Placing some thin foam rubber between the fuel tank and any parts of the fuselage which might touch it usually eliminates this problem.

Finally, fuel quality... Glow fuel is mostly alcohol, which likes to absorb water and when it has absorbed, it won't run very well. Any cloudiness in the fuel usually indicates it has absorbed water. Nitromethanol is added to our fuel to get more power than pure alcohol. The nitro will evaporate more easily than the alcohol. If this occurs, your engine will probably run after adjusting the mixture needle, but it will seem to lack power. Cure for either problem is to get a new jug of fuel.