Rm 125 1986 Low end problem

Hello , I have a RM125 with a 1985 motor and I kinda have some problem with the Low end power , when i hit the power band its just perfect but whenever i go trough a hill the motor start to goes down the the low end and then miss power to stalling if i dont hit the clutch, what could be my problem , also its has a rought idle and its hard to start when its hot, and i my carburetor has been clean , but its old... so i was maybe thinking of buying a recent carburetor like 2000 model... dunno

this year of motor have no powervalve so it doesnt help getting more low end and i think the first gear is too long maybe thats why i have so much problem....

by the way thanks