On the straight pull version which comes from the electric start Homelite weed whacker, the channel for the pulse signal comes mighty close to the throttle bore (especially on a bored out one). Be careful of this fact. The regular insulator doesn't seem to get into this problem when bored out.

I know from personal experience, a machine reamer doesn't do well for enlarging the hole because the plastic will tend to expand when the reamer is in it. I use the angle pull models and they came from Carr already bored out.

Compare your old one with the new one.

Enjoy,

Jim