where is he knock sensor on st170

[hondacr250]

hi

i ran out of petrol last week in my st170 and eventhough i got it started and been driving it around and it seemed to be ok but then the engine management light came on with the code PO325 knock sensor 1 circuit (bank1 or single sensor) circuit malfunction.

if any1 knows where i can find this part under my bonnet much appreciated if you could tell me.

thanks