Before I fit a cap and needle I always test them, because there is some differences in the caps and floats. You have to make sure the float does't hit the tower section the needle sits in, some do some don't. If the float hits this will prevent the float shutting the needle off. To be honest yesterday as I was rushing, I am not sure if I checked the 2 that flooded badly, I was swapping bits around trying to fix the problem and in the end I gave up and took a new cap,needle and float off another mower I had running earlier in the day and that fixed the problem. One thing I have noticed is that when testing these new caps and needles, some stick up some don't. At the end of the day these needles are 99% better than the plastic ones, most of which don't work
