lgmac if your tank stopper is cracked then do not fly untill you replace it. I recommend you replace the entire tank though and change to one of these:
http://www3.towerhobbies.com/cgi-bin...&I=LXK831&P=RF
Its a Hayes and you will have far less problems with this type.
Now this has gotten confussed, what airplane are you running in a parking lot? Operating a glow powered airplane in a parking lot is a really bad idea, This whole parking lot idea with this airplane is quite disturbing even if you do not intend to fly. Are we talking about that older P-51 arf or are we talking about the Eagle trainer?
Please remember if you try to fly it without help i.e. an instructor on a buddy cord then this airplane is not likely to live more than a minute or so.
John