That is definately not a honda mate, its either a yanmar or a chinese copy of a yanmar ie changfa 186f, by the look of the frame it is a titan pro or something similar, maybe a jetmac, a quick way to tell is the sticker behind the cooling veins, or even the throttle control, although the throttle controls on genuine yanmars sometimes break and are replaced with aftermarket throttle controls so thats never a dead cert... defo not a honda diesel though mate, hes telling you lies straight away