Ignorant people freely dispense all kinds of bad advice; that's nothing new and heat riser valves are no exception. A lot of guys think the manifold heat is nothing but a cold-weather assist. That's wrong. Fact is, it is greatly beneficial (if it's working correctly) no matter what the weather or climate. This 1935 Jam Handy cartoon would be a real trip to watch even if it didn't contain a sequence (which it does, at 5:37) specifically and correctly answering the question about the manifold heat:
Below a certain temperature, gasoline is a liquid. Liquid fuel does not burn. Only vapor burns. The latent heat of vaporization of gasoline works to cool down the intake manifold even as engine heat works to warm it up. The debate is whether it's necessary to apply heat to the intake manifold. There are opinions "yes" and "no", and there are varying levels of understanding of how the system works and why it's there, and the right answer also depends on the engine configuration and vehicle purpose. I don't mind saying I have a very complete and accurate understanding of how and why the system is there, and my opinion is that on a street-driven vehicle in any climate with a non-race engine, an intake heat system should be in place and working correctly for best driveability, performance, and fuel economy. On a street-driven vehicle, intake manifold heat only makes things better, not worse. Removing or disabling it means sending liquid gasoline into the cylinders. Your engine will produce less power, use more gasoline, foul the spark plugs faster, wash oil off the cylinder walls, and degrade the engine oil faster. But on the other hand, you get to go on the internet and brag about how clever you are for disabling the valve, so it's a tough choice.
