If you haven't overheated the engine badly by using a fuel with too little lubricant, you should be able to break in the engine as the directions tell you. That should solve the problems a lot of folks have been having, although we have found that the run does continue to improve with further running while flying.

One modification we did make was to add a nickel to the weight spot on the lower side of the outboard wing. We haven't had any problems with line tension in winds under fifteen miles an hour. Cox used to say that if one could see the leaves moving on trees, the wind was not too strong to fly their 1/2A models. However, if one could see the even the smaller branches to which those leaves were attached, there was too much wind to fly them. This latter condition is far less wind than the fifteen miles an hour we set as a maximum for the Hyper Viper.

The plane is just a flat ball to fly!