I posted this on the slantsix.org so why not here.

Ambient temp 76*F

72 Duster slant. I ran my fuel line over the valve cover and removed the factory line. Just idling for 10 minutes, hood open. Temp check with a lazer? 98*

74 Dart stock idled same time with hood open.

189*F!!!!

If you wonder why you have hard start problems when hot? There it is!

Why would that cause a hard start. You should be starting on the gas in the carb not the line.

Not choosing sides, here.

Might be talking vapor lock.

If you are dumpin hot fuel in the carb then shut it off it will boil out of the carb pretty quick, at least the lighter molechules that light up easy. Plus cranking it makes the fuel pump pump all that vaporized fuel through the carb before the liquid fuel gets there. That is vapor lock and that is why you can get hard starting when hot.

I long ago rerouted my slant's fuel line to be clear of the hot stuff in the engine bay. Routing it well also makes pulling the valve cover easier.

Be very careful of temperature readings from your "lazer". That laser spot is just an indicator, not part of the measurement, and may or may not be where that sensor is looking. Most of those gun-type infrared temp gauges are not adjustable for emissivity or reflected energy, either.

Here are a couple of thermal images of a running slant. White is hot, black is cold. The exhaust manifold surface temperature in these shots peaks out at about 331F.

When you start a stock slant hot you hold it on the floor until it starts. It boils out of the carb, floods the motor. I had that problem in 50* weather with my stock 198 in the Duster.