If I grind down the alluminium mount spacer evenly about 1cm will this cause any issues (this will help with clearance issues on my large frame mtb ) 66cc 2 stroke
You should be okay. The air filter may be a little close to the seat tube. (depending on what style filter you have). You may have to install the filter after installing the carb...as opposed to installing as one unit.
I shortened the rear mount for my engine by cutting about ½ inch off with a hacksaw then cleaning up the cut with a file and sandpaper. Cuts easily and works fine in my application (see pic). The mount may be a little weaker with respect to bending, but it isn’t subjected to that kind of force if the seat tube fits properly like my case.