Recently, I've been working on my friend's Vespa 150 Sprint. It has been in storage for a long time, and now wanted to get it roadworthy again. The main problem that it has had, even in storage, was that it leaked oil - bad. It was two stroke oil, not case oil that leaked out. All the largeframe Vespas in the US market in the 70's had oil injection. This one had a problem keeping oil in the tank. It was a slow leak, but over time, all the oil came out. So now, I had to determine the cause of the leak.
My first thought was that there was a crack in the tank, sight glass, or oil line. I pulled the seat off and got the tank off.
When I got the tank off, there was no problem with anything in there. As you can see from the above photo, there was no oil inside the frame. The metal oil tank was fine (the oil tanks from the pre-P series were metal, not plastic), the oil line was fine, and the sight glass was not cracked. I did notice that the fuel line was hard as a rock. Since I was already in there, I replaced it.
Next, I turned my attention down the line, the oil line, that is. I couldn't find any really obvious culprit. When I took off the carb and looked in the air box, there was nothing that jumped out at me. The only thing I noticed was that the screw that holds the air box on the case was a bit loose. I tightened it up. I think that the air box was not 100% tight on the frame, and oil was leaking out from the bottom of the air box. Since I have tightened it down, the scooter does not seem to be leaking. I'll keep an eye on it, but for now, I think it is problem solved!