i have a 2002 yz125 as well. .42 kg. fork springs, 4.8 kg. rear. 50 tooth rear sprocket. motor is all stock, have the updated needle from yamaha in 1st clip position. works great.
tried the v-forced reeds and was not impressed. i didnt feel any power increase anywhere in the rpm range nor did i feel the claimed more over rev. jetting felt fine. called them and asked if there were any jetting suggestions. they told me to use what i have in there. maybe someone else on this board has had better luck with this product. my opinion, is to save your $140 and keep it for wearable items such as tires, top ends, chain and sprockets. keep practicing cornering techniques to improve lap times and overall speed. that won't cost you anything. it's free speed.