I am trying to fix up this old outboard, perhaps to sell. It ran fine till one day about 4 years ago I couldn't get it to start. I opened the cover and pulled the rope. To my surprise something broke off and fell into the water. I never got around to looking into this until now. I have circled the area where the broken mystery part fell off. I could not find this in any of the online blowup diagrams. 
