[Firebirdjones]

Lots of things cause vapor lock, and there are ways to prevent it.

In Michigan this time of year isn't unusual to see vapor lock if you have one of those unusually warm winter days. I lived in Ohio and know how flip flop the weather can be.

During winter months they use what is called a winter grade fuel to prevent fuel line freeze up. The problem with it though is the additives used cause major vapor lock headaches when the temp even reaches 50 degrees. To top that off, they don't switch back to summer grade fuels until April when areas like Michigan, Ohio, Indiana can already see temps in the 60's or more. Top it off with a continually degrading quality of fuel with 10% (or more) of ethanol added and it compounds the problem. A real pain in the ass.

Things you can do to battle vapor lock...

Biggest and most effective.....Run a return style fuel system. By 1971 this became pretty much standard issue on most vehicles so you should have it on your truck. This keeps the fuel moving in the fuel lines (up to the pump at least) so it isn't sitting stagnent in the system and attracting heat. The only stagnent fuel in the system with a return style fuel pump is the line from the pump to the carb.

Make sure the line from the pump to the carb isn't touching anything. At least a fingers width from things like the cylinder head, water pump, thermostat housing, intake manifold etc....

Run a higher octane fuel. You spend more at the pump, but the lower octanes have such a low flash point they are more susceptable to vapor lock.

Run a heat shield under the carb if you wish. This will slow down the process of radiant heat reaching the carb.

I also use a thick carb gasket (not the paper thin junk) Usually 1/4" thick, can be found in any parts stores. This will help as a mild heat soak.

If you can get away with it, I block off the heat risers to keep the intake manifold cooler. Worked fine for me while living in Ohio even during cold months. Does make some cars finicky however on cold start up.

I also prefer to run a cooler thermostat. Keeping the engine cooler means cooler underhood temps.

With all of these little tricks done, you really shouldn't have a vapor lock issue. I don't see it even in 110 degree heat here in AZ with crap gas, no fancy cool cans either.

If you run an electric pump, vapor lock becomes a non issue, because they push fuel much better and usually at higher pressures that require a regulator.... Stock mechanical pumps suck fuel and generally are lucky to generate 6 psi of pressure.