Vespa suddenly starts sucking after some riding

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?

Re: Vespa suddenly starts sucking after some ridin

how good is fuel flow from the petcock

Re: Vespa suddenly starts sucking after some ridin

Flow from the petcock is strong, way more than a 78 jet is going to burn. If it were a flow issue I would expect the banjo connection on the carb or more likely the tiny fuel hole that the float needle blocks.

Re: Vespa suddenly starts sucking after some ridin

james you still have that 13.13 carb and 65 kit if so your jetted way to high. My bet is your fouling out the plug and prob flooding the engine

Re: Vespa suddenly starts sucking after some ridin

but yeah didn't finish. Pull the plug is that shit black and try and if the tip is black your fouling the plug.

The condesnor could be bad. I would check jetting first it sounds like your fouling out the plug.

Re: Vespa suddenly starts sucking after some ridin

Nah, plug looks great.

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Re: Vespa suddenly starts sucking after some ridin

hmmm, is your head dirty or is oil climbing up the threads it shouldn't be.

Check points and condenser you prob should of replaced both when the motor was out so iono.

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