I've received a brand new .55-AX on a Friday after leaving work, bolted it on that evening, started it quickly to make sure it works then shut it off immediately so I didn't bother my neighbors. The next day I went to the field, set the needle slightly rich and flew 4-5 times that day without any problems at all. I'm not saying that it doesn't need to be broken in but it isn't as critical as it might be with other engines. I think yours just has a problem or defect. Either the cylinder head is coming loose, there is a problem with the piston or cylinder or something like that causing compression loss. They are good engines but even the best stuff can have problems from time to time. Nothing is perfect unfortunately.

You might be able to stick your battery way back in the tail to make the .75 balance. If you do get it to work, the plane will be ballistic. That's not necessarily a bad thing.
<br type="_moz" />