I have to differ with you. I don't post much in the forums but I think you need to look in the gas engine forums and see all the problems AND crashes they are having with thier so called R/C engines.
I'am some what new to these conversions and have many built for R/C engines but the ones I build some to be as good as and some times better. I to this point have only built echo, husky and sthil but they are as good as the ones you refer to and maybe better.
I've had more problems with the production engine than my own so figure that out.
I will agree that some try to convert weedeaters that already have a problem and don't know how to solve the problem but they WILL figure it out if they keep trying. The only thing they are fighting is the weight to power problem.
I just built a 13.6 cc echo for a Senior Kadet for the kids and who ever that is checking out great on the bench. Tell me a production engine that I could buy in this size range.
Again I think you need to look at the forums on the production engine and see ALL THE PROBLEMS they are having. Best Ron