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MG MGB Technical - Vapor Lock: Wrap the Header?

I still have a vapor lock problem. I installed a glass see-through fuel filter just forward of the rear carb, which is a great diagnostic tool. When the engine and weather are hot, the filter housing will be almost empty of fuel. The result is misfiring from fuel deprivation. If I loosen a fuel hose to a carb, air will hiss out and the filter housing and hose will immediately fill up with fuel. I'm using a new SU pump. I was told by one person that the fuel is vaporizing in the float bowls. I have an upgraded heat shield installed with the original heat shield, but it's still mighty hot around that area. Now, I'm tempted to wrap the header with that fiberglass-looking tape that's made for the purpose. Any thoughts on this from anyone? I thought air was supposed to vent out of the tops of the float bowls.

thanks for your input,
Tyler
Tyler

Tyler - check your carbon cannister. It may be plugged up & in need of overhauling.
David

Tyler - YOu might want to check into having your headers coated with the Jet-Hot coatings http://www.jet-hot.com/
I have not personally used them (yet), but a number of people who have had manifolds or headers done have reported excellent results. Good luck - Dave
David DuBois

Tyler-
Wrapping the header will only result in a warped header. The fact that air hisses out of the line when you loosen it is significant, but we need more specific information: What year is your car? Which engine do you have?
Steve S.

Can't see how vapourising anywhere between tank and float chamber can happen. Once the fuel level in the float chambers drops the float valve opens and any air in the system will hiss out then, being replaced by cool fuel. I very much doubt that your lines are getting hot enough to vapourise fuel faster than the pump can pump it. Sounds more like the pump is sucking in air.
Paul Hunt

Air hissing out of the line? The line should be pressurised against the needle and seat (or grose jet) inside the float bowl. That's not abnormal. However, one would rather that fuel hisses out, not air.

I'm no expert, but vapor lock as I understand it affects the "pulling" side of a pump. It's much more common on motors where the pump is physically attached to the engine block. The pump gets hot, fuel vaporizes and makes bubbles in the supply line. The pump tries to pump air, but just stretches the air bubble against the resistance to drawing fuel up the pipe out of the fuel tank. When the pump is way back near the tank, like in an MG, you tend not to have the problem. Any air in the line gets pressurized and pushed to the highest point (your fuel filter?). n spite of the air, fuel can still be pushed along because the pump valves are still immersed and making decent pressure.

Sorry, that was a long way to go to get here. If I were you, I'd not focus on the heat in the engine compartment. While the MGB is not the coolest running car, it does work as designed.

Could your fuel pump be starting to peter out, exhibiting these symptoms as it gets hot? Are the air vents to your fuel pump clogged, and so not letting the diaphragms operate fully? Could you have a leak in the rubber line between tank and pump? Is your fuel tank ventilation system plugged, so that the tank develops a vacuum after a period of running (the infamous gas cap "whoosh")? Has your fuel tank pickup become dislodged, so that it isn't always sitting in the puddle of gas?

Sorry to be so wordy. Must cut back on the coffee a little. And please note that nearly every word here is either opinion or conjecture.

Best of luck,

Matt K.
Matt Kulka

This thread was discussed between 20/10/2002 and 21/10/2002

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