Ep. 4.31 "Br-Rooom! Br-rooom!" (May 12, 1965) is all about Rob buying this motorcycle, against his wife Laura's wishes. There's a scene from this episode where Rob and Laura's son, Ritchie, sits on the bike and pretends to ride it. It's the closest shot of the logo I ever got. Just taking a shot in the dark, I don't know my mopeds...1965 Harley Davidson M50? Found some on the internet that look an awful lot like this one, gas tank logo and all. The more I look at it and look into it, the more I'm convinced this is a 1965 Harley Davidson M50. Here's a link to another one. Link to "www.khulsey.com"
Agree: 1965 Harley Davidson M50
