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The Flathead Vapor Lock

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In this Tech Tip, John makes a few suggestions on how to deal with the classic problem of a Flathead Ford, vapor-lock.

Flathead Ford won't run when it's warm

“Hi, I own a ‘51 Ford convertible that I cannot get to run in warm weather. The fuel system shuts down what is your fix for this problem? Fuel pump? Carb? Frustrated owner here, thanks for any help.”

  • Jim

Hi Jim, Your question brings up the age old problem of keeping the Flathead Fords running in warm weather. The Flatheads were notorious for vapor-locking. Unfortunately, the warmer it gets the worse it gets. The old trick of clothes pins on the fuel line and aluminum foil over the line always doesn’t help. Vapor lock and boiling fuel is normally the culprit. First you need to check fuel flow to make sure everything is flowing freely in the fuel lines. If not, make the changes to correct those problems. If you have 6 volt pump you can look at P/N 9104259, or a newer mechanical pump will insure flow. Keep in mind the ‘51 mechanical pump has two possibilities for the pump fittings. A regulator such as 56058500 is always recommended with electric pumps. If your mechanical pump appears to be working, maybe a helper pump is needed. In that case we offer P/N 465810400 in 12 volt and this requires no regulator. Carb spacers help such as P/N 91011615 and sometimes customers will use 2 per carb. Thermal sleeve is available under P/N 70414030 and others. Relocating the fuel line so not to be close to the exhaust is another good idea.  Run regular gas without ethanol and avoid the blended fuels. Feel free to visit us on the web at or call 1-800-979-0122 with questions or to place an order.

  • John W.

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