High grade gas won't make it easier to start. It might actually make it more difficult to start because of the higher octane level, especially if you have a weak spark. That engine only needs 3 things to run. The right air fuel mixture, a good spark, and good compression. If any one of those things is not up to snuff the engine will not run properly. The first thing I would do would be a compression test if you can get the motor warmed up a bit. Perhaps your mechanic friend could help you there. If your compression is low, or varies greatly from cylinder to cylinder, it will be difficult to start and keep running just like you described.