Yesterday I drove my 57 pickup about 15 miles downhill to a meeting at highway speed and it drove fine. The engine sat and heat soaked for about 45 minutes. Coming back uphill was a vapor lock nightmare. I had to pull off the road 6-8 times to allow the percolating fuel in the carb to cool enough to continue. By "uphill" and "downhill" I mean an elevation change from about 7600' to 5400' and back again. This is on a stock 235 with the one-barrel Rochester carb and mechanical fuel pump. The temperature was in the 60's. I could see the fuel vapor bubbles backing up into a glass-bowl fuel filter just ahead of the carburetor so I know that the percolation was in the carb bowl. Engine temperature with a 160 degree thermostat was below the halfway hash mark on the temperature gauge so the engine isn't running particularly hot. To combat air pollution, Colorado mandates a "winter blend" of gasoline that vaporizes at a lower temperature and that is what is in the tank. My fuel pump is working at 6 psi. A new rebuild kit was installed in the carb a couple hundred miles ago.

Before I go through the effort to re-plumb the fuel line between pump and carb to relocate the glass bowl fuel filter and avoid as much engine heat as possible, or add an electric fuel pump, I'm wondering about an easier fix. I have a spare carb (or two) that has a small hole drilled in the top to vent vapor done by some unknown frustrated driver some time in the past. I could see the possibility of introducing contaminants or the likelihood of the fuel in the carburetor bowl evaporating more quickly in a parked vehicle. What else am I missing?

My other trucks all have 235's in them and the hassle of vapor lock is always possible at my high elevation and during summer heat. But with Fall temps in the 60's and the winter fuel blend this is a bigger problem than usual. Is there anybody out there running a 235 with a vented carb successfully? I'm open to suggestions. Thanks!

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