I used H1R for the last two summers with no problem at all at a 40:1 mix, this summer im using yamalube 2R, only because my source for the belray closed up shop, only thing i noticed was a build-up of carbon in my fmf pipe that was pretty tough to get out, but id think no matter what full synthetic you run youll have that, just normal, hot gasses hitting the colder header causing a build-up a bit of oven cleaner fixed that. im always a bit suspisious of any mechanic that blames things on oils especally full synthetic ones, id look at the jetting or the float level ect.. id suspect something mechanical before id suspect bad oil, just my 0.2