425 governor spring

I have a 425 that when I mow for over two hours it starts acting weird. It seems like the governor will allow the engine to rev up then load up and slobber then repeat the process. I have put new coils on it, rebuilt the carb and tuned it per the manual. I also changed the Time Control Module. I did notice that the spring M97354 was broken. Would that cause the problem? Thanks for the help.