I just got my Sts .28 and I got the gpm mount with it, The person at the R/C mall in Hong King said I needed it, well if you run a 19 tooth CB and a 49 tooth spur, with the hot bodies side plates, and original ,(but if you run a 18 tooth CB or smaller it'll be fine)you will need to dremel a spot on the plate so the engine can move to the side more and foward! Engine so far ran great! Installed it and primed it 1 pull with my finger over the exhause , and it fired up on 1 pull.. My big problem right now is, I have the Ofna aluminum 3 shoe clutch, and it seems to slip a lot, anyone have a better clutch shoe set up?