The EFI myth
Possible fix: carb spacer. Either plastic or wood. If no room for that, the thickest foam or cork gasket you can find. And a heat shield. And if you're not running one, consider a ThermoQuad.
With and without, no change. Tried phenolic, wood, plastic, cutting boards, aluminum, you name it. Tried every type of heat shield, wrapped the lines (fiberglass socks, alum foil, combinations of both, heat-wrap, changed fuel line locations, etc). No changes. The carb simply got too hot.
I'm dealing with the same exact situation now on a second vehicle. If it's hotter than 90F outside, I get into vapor locking, boiling and percolating bowls, etc. Fuel is delivered by an electric pump, fuel line is completely isolated from engine and isn't near any heat sources. I've lowered the floats, tuned the timing and mixture for coolest operation (stays at 180-190F with a 194 thermostat, only gets to thermostat temp if I climb a decent grade, never gets hotter than 200F). Carbs are on spacers (but I have a significant hood clearance challenge, so they're only .250 thick). It's also got three electric fans. If I let them run after shutdown, I can avoid percolation about 60% of the time. Nothing else has had any appreciable effect. I'm about to try a 160F thermostat to try and keep the intake cooler to prevent heat soak into the carbs. I can shut the engine off, disconnect the fuel, and wait 5-10 minutes and watch the fuel boil and then fire out of the boosters (it's worse if I leave it connected, but disconnecting rules out the line as the cause), then listen to it whistle and spit for a few minutes before the entire garage smells like gas. It's awesome.
So far, the experience with this new engine has been the same as what I had with the dart. Except the new engine has holley carbs (2x4) vs the single edel carb on the 318. The edel made it easier to see the boiling fuel - I could take the top off and watch it.
When it was cooler weather and more humid, it didn't seem to be as bad. But now that it's hot and dry, it's a challenge.
Doesn't seem to make a difference with my stuff. Typically it's the needle and seat that get gummy. Best solution I've found is to fill things up a few days before use and let them soak, then run them hard and hot for as long as possible during first use. I've tried seafoam, sta-bil, and a half dozen other things over the years. It helps with the gas in the can, especially if it's not totally full. Mostly seems to help keep water out. Some of the 'stabilizers' turned to glue if the surrounding fuel evaporated - that really sucked.
I have found draining is probably a bad idea. The contrary-FILL the tank with gas treated with Sta-Bil or StarTron.
I used to do it that way. Works with dry air, but not now where it gets humid. 90% of my issues are caused or made worse by humidity. If left completely full, I come back 5-9 months later to lots of varnish and about half the fuel I had put in. If it's only for a week or so, and it's not 100+ degrees, then full is better but not perfect. Still lots of popping and farting and not wanting to take throttle until the fuel washes things out a bit. Sometimes that's a few minutes, sometimes it's hours.
Definitely need different storage techniques. As I said: tanks FULL and treated. Worked for me for years. My elderly mower fired up the first time every spring.
I'll start a go-fund-me for a heated shop ;)
I agree that different conditions would help, but I'm not moving back to the desert and heating my shop won't be an option for quite some time. The stuff at the second property won't ever sit in conditioned space, and the humidity there is far worse (plus it's near a salt water coast!).
