No or low compression, hard to start, will not run properly. The first one is a dead give away the other to can all so be caused from other problems like tuning, air leaks and so on. Most motors will last a minimum of 5 or 6 gallons of fuel and have heard of engines run as much as 10 to 15 gallons.

The best way to check a motor after you have some time on it is to take it apart and check it out. Are you having a problem and if so more information would help in assisting you.