Hi, could any one tell me what the maximum size is you can increase the bore to on carbs from a 21? I know they have to be D shaped but wondering what increase can be expected from any such mod?
The reason behind this is i wish to retain the oil pump for ease of use but get as much fuel as possible in to my 300 motor.

Also i have the shorty style of plug [NGK 95] fitted to my 300 kit but what is it partner in the normal style i.e. BR9ECM or BR10ECM?