Alright guys...what kinds of things go wrong after some minutes of riding, say between 5 and 10. My kitted Vespa Grande goes like a scalded dog when I start it up, but after about that much time it slows down noticably, from 40+ to maybe 30. It happens suddenly, and sounds kind of like it's bogging. When this happens it also gets like a flat spot in the throttle, where the engine sounds barely alive around 1/2 throttle. If I go WOT it sounds better, but still only goes about 30. If I turn the bike off for even 30 seconds it seems to do fine again. Any ideas what this could be? So far the only thing I can think of is either I'm burning mix faster than it's making it into the carb, or the condenser is going. I guess theres always the spark plug, too, but it's a B8HS thats only been in there for about 40 miles and is surgically clean.
What else besides those things break suddenly during rides like that, and go back to normal just as quickly?