Normally, the petcock has nothing to do with fuel regulation. Some have a priming position, but I doubt the peugot does. The fuel is regulated by the float and needle in the fuel bowl. When the fuel bowl empties, the float drops down, which drops the attached needle and pulls that needle away from it's seating position, letting fuel into the bowl. Once the bowl fills up, the float rises and pushes the needle back into its seating position, sealing off the fuel flow until the amount of fuel in the bowl is lowered again.
It might be a misadjusted float level or a dirty carb. Did you clean your carb out thouroughly? I don't know my peugot's very well, so I couldn't tell you how to adjust the float level (if that's the culprit), but the carb should be cleaned, priority #1.
But now that you have spark, it should be relatively easy to get running!