Posted by Rick Hogan on Saturday, July 07, 2001 at 1:58AM :
In Reply to: 315 Poly Tuning Specs posted by Russ In Seattle on Friday, July 06, 2001 at 6:52PM :
Vapor lock is fuel reaching its boiling point inside the lines or pump, in some confined area. When fuel boils, it acts like water in that it turns to steam, or vapor.Not only will the pump neither draw nor pump vapor very efficiently, the fact that it is expanding all the while fools the systems into acting as though fuel is moving. The carburetor fails to maintain proper bowl level when vapor is entering instead of liquid, so it essentailly starves. Only liquid can be atomized by your carburetor. Vapor lock is caused by heat, specifically under-hood, engine-related heat. Hot exhasut, either from a conponent too close to the fuel, or blowing at it from a leaking joint, is the leading cause. Radiator air can do it as well. Look for any fuel line or component in the path or proximity of the flow of heat. Constrictions are highly suspect. I have a pressure regulator on my 71W200/383 that gave me fits before I simply moved it behind the heater hoses to shield it from radiator wash. The fuel wouldn't boil until it left the orifice of the regulator, then it was the resultant reduction in pressure that allowed the boiling in earnest. It's just like if you popped the lid on a pressure cooker or the radiator cap in an overheat condition. The pressure raises the boiling point, and its release pemits boiling. The same conditions exist in the fuel pump, to a certain extent, so that's why they are so susceptible. Pressure differential, man, it makes the world go 'round. Reroute, shield, reapir, feel around for the hot spots in the flow(be careful), and study your fuel system carefully. It's all phiysics.
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