[AZKen]

Some folks say the fuel has been reformulated and vapor lock is back. I have not heard anyone here in Phoenix complaining about that or read anything on forums much. I'll keep an open mind on it. It does exhibit the same as vapor lock but it also acts like the other items I mention. All I know what to do is experiment to isolate the problem, to eliminate causes and test fuel delivery system components. Take off the filter between pump and carb in case it is acting like a boiler vessel from block heat/fan heat. Run a straight hose from pump to carb. You seem to have insulated the tubing. If your fuel pump is the slightest weak, it will either not deliver enough fuel or not enough pressure to overcome vapor lock if it's vapor lock. Be sure about the fuel pump. Make sure your insulation technique hasn't added heat and is conducting heat toward tubing. I think a separate, non touching shield, set to catch air flow would be WAY better. Just an aluminum .060 sheet running parallel to frame allowing air flow to pass on both sides. Almost like a boxing plate. When did you add the wrap on tubing? It would be pretty interesting to use an infrared, laser aimed thermometer, pointed at various points on the fuel line to spot a big spike. Do you have a heat riser on that side? if so, if it's sticking it will heat up, it's right there near fuel line? and maybe your filter. GET RID OF IT. Don't need it in AZ. If it's not sticking, it's mass may still heat the area.
P.S. Hope you don't have a chrome ignition coil. Hope your coil is not touching block directly.
Trying to get a feel for a problem from afar is the hard part. You are providing good clear info. Keep it up. Sorry Mcgee.