See if the chain is rubbing the inside of the derailleur cage. My guess is that you don't need larger pulleys, you need wider ones. Never worked with Huret pulleys or derailluers but the old Bullseye and Carmicheal replacement pulleys were narrow (narrower than the Suntour pulleys) and came with washers for widening out the derailleur cage to prevent chain rub. If the chain isn't rubbing the cage can you post pictures - one from the back and one from the side?
'84 Trek 660 , '88 Trek 1500 ,'89 Trek 400 , '97 Trek 720 , '99 Trek 2200, '02 Trek 520