The YF was used on a lot of engines and they were good carburetors. However, the 4480S is for an engine about 10 years newer than yours. Mixing and matching things is not always good. The initial timing should be set with the vacuum line disconnected and plugged. If it runs good with the initial timing and then doesn't run right with the vacuum hooked up, something is wrong. Either the carb is not matched to the distributor or you have a hole in your vacuum chamber and you are creating a vacuum leak.