i have a 7 speed shimano freewheel setup . i broke the derailleur that came with mine so i ordered a replacement and it is a 6 speed . i searched in google and it said that it is perfactly fine to use it in this situation . so i follow through the park tool rear derailleur adjustment video and it doesnt seem to work . when i adjust the barrel adjuster it works in the small cog but when i go up the cassette it becomes increasingly difficult . i tried everything from limit screw adjustment and everything i even tried doing a backflip , nothing worked . help me please!