Quote:
Originally Posted by Ghostrider 310
Someone else will explain it far better than I but in general it's a heat induced, if the cap isn't venting it can build up and stop fuel delivery. What you are describing sounds more like a vacuum leak.
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You're confused about a number of different fuel related issues.
Vapor lock has to do with heat, atmospheric pressure and the vapor pressure of the fuel being used (it's just one of the reasons why some airplane engines cannot run auto gas) Vapor lock occurs when liquid fuel vaporizes with in the fuel system and the fuel pump cavitates due to any number of factors like heat, low pressure from a partial inlet blockage, or a "soft" pump that creates a pressure slack in the system by not maintaining constant pressure...or some combination issues causing the fuel system pressure to fal below the fuel's vapor pressure.
All the gas cap vent does is equalize the internal tank pressure to ambient.