Try taking the pull switch off and polishing everything up and reassemble.  Make sure all connections are clean and tight.

AaronSEIA

Usually, what happens is the square contact on the switch side is worn or burnt to where good contact with the Starter pad is starting to be a problem. This is a high amperage point, and good solid contact is important to transfer high current to the Starter motor to engage it. If that's the case, a fireworks show is usually the norm as you have. Sometimes if the square contact isn't to worn, it can be cleaned up or rotated to the better area on the contact. If its pretty much toast, you have two ways to go with it. Either replace the mechanical Starter switch with a good USA made unit, or move to a Starter Solenoid either key crank actuated or button. If you move in that direction, the Starter motor contact pad will have to be changed to a stud to accomodate the Starter relay which can be mounted right on the Starter motor. This means you need to go into the Starter to make the change-over. Its a little more work, but that's really the way to fly from a reliability standpoint. We still have  quality USA made switches in stock if interested if just changing over the switch is what you rather do. We offer Starter motor services also....

Steve@B&B

Ya think?  I say yes! 

At the bare minimum, the contact on the starter needs a good filing, get it down to clean copper, and put a new switch on, or upgrade, as steve says...