Re: 1948 flathead 6 problems. Help!


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Posted by Tom in Oregon on Saturday, February 25, 2006 at 12:53PM :

In Reply to: 1948 flathead 6 problems. Help! posted by mark on Saturday, February 25, 2006 at 10:47AM :

My '53 B3 flat fender PW often gets vapor lock when it is hot out. I use a 6V electric fuel pump with a regulator and filters. My tank was cleaned about 10 years ago. The fuel line goes near the manifold, but is as far as I can get it. No heat shield per se. I also have a NOS mechanical fuel pump on the block, unconnected, but with lines and fittings to allow quick change over in case the elec. pump fails. I burned one up about 6 years back after running out of gas, so that failure was partly my fault for letting it over rev.
Anyway, what I do to stop the vapor lock is keep a rag wrapped around the hottest part of the fuel delivery line, and when the elec. pump starts over revving, I get out and dump water onto the rag to wet it out. The evaporative cooling seems to always do the trick. If I don't have any water it takes a while sitting to cool down enough. I have never been desparate enough to have to pee on the rag! The fact that the wet rag stops the over-revving pump seems to verify my assumption that it's vapor lock. I have considered putting the fuel pump (or an additional one) back at the tank so as to push the fuel past the manifold area rather than pull it, but for my use the wet rag method has been sufficient so far. Funky and requires intervention, but cheap and easy. The hardest part of the fix is hearing the fuel pump over-revving above the din of gears and rattles, and of course the engine noises. If I don't hear the pump first, coughing and missing soon follow to alert me to the vapor lock.
Hope this helps, but your issue could well be due to some of the other theories presented below.
By the way, do you suppose there is any problem running the NOS mech. pump dry all the time? I assume flapping the diaphragm without fuel in the pump won't wear it out any faster than if it were pumping fuel instead of air. I put the in and out lines together to keep dirt and dust out, so it just pumps air in a circle. I suppose I could pump fuel or oil in a circle to keep the diaphragm wetted, if it is deemed safe and good for the pump longevity. Opinions?
Tom in Oregon



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