Yes, the generic bags that take the F&G are known for cutting down the suction of a Kirby, and they look strange.
The original correct bag for a Kirby Classic model 1CR would have been the gold cloth bag, with the Sani Scraper pocket in back, with the leather CLASSIC patch in front. These are NLA, but gold colored bags as well as red, blue and black replacments can be had on E-Bay.
When sending a Classic in for a Factory Rebuild, the Factory is replacing all models that used the original Sani Emptor(shake out bag) System with an all black fabric bag.
If you want the filtration and convenience of a paper bag system, id recommend the Mini Emptor System used on the Heritage 2-Legend 2 machines, with the Silver/Gray Heritage 2 bag and G Series fill tube adaptor inside to take the G Series Hepa Bags. This is what i have on my Classic 1CR, and it does NOT cut down the suction power at all that i can tell. Plus the Silver/Gray bag looks sharp on a Classic machine. ( In MHO anyway)