Can anybody solve this hot start issue? I'm out of ideas!
Yep been through all that.
Insulated the line, and routed it as far from the engine as possible.
Electric fuel pump straight to the carb with rubber line.
My fuel pump is under the passenger floorboard mounted to the side of the subframe connector.
System does not build pressure when the car is off as it acually drains back when off. (I know this becuase when I turn on the key I can hear the pump pressure the system back up) so I know it's not a needle/seat bleed by problem.
The vapor recovery system does not circulate the fuel that is already in the bowls and this is where the actual problem is.
Have you noticed how the car runs like crap for a bit even after it does start? Most of us have that.
It seems that it clears up after the carb gets new fuel from the line.
If you rev it a time or two the new fuel gets there quicker and it clears up quicker. (Gotta get that hot fuel out of the bowls)
Holley carbs have the benifit of the cork gasket between the body and the bowls as well as the bowls being farther away from the main body.
You said,
"I expect that when I remove the mechanical pump, and get the line fully insulated, as well as a little shield between the line/ headers, even this will improve."
I hope you are right but I kinda doubt it, since the problem seems to be caused after the fuel is already in the carb and not because it being heated in the line.
Overall it's only a quarter of the year or so that it's hot enough to do it, but it's still a pain in the *ss I'd like to solve.
I think the cause is probably simpler than you think. The 4140 style Holleys have the float bowls up away (not in contact) with the manifold, and surely must get SOME airflow, as well as "not so much" conduction through the metal of the manifold/ carb
Edelbrock, on the other hand, is just like a pan on a stove burner.
What you guys discussed in your referenced thread is pretty much just what I did:
Electric pump
Do the best you can with insulating/ rerouting the fuel line
Use a carb spacer/ and insulator
Install a vapor recovery system. The vapor recovery not only keeps a small amount of fuel circulating, it also nearly immediately dumps fuel pressure in the line to zero on shutdown, and provides a path for boiling/ pressure buildup, so that fuel is not so badly forced past the needle/ seats under pressure.
I still have not .....uh.... "finalized" my fuel line routing, and am presently running the electric pump through the mechanical. On very hot days, it sometimes STILL requires a part throttle, 5-10 second crank, but this is intermittent.
I expect that when I remove the mechanical pump, and get the line fully insulated, as well as a little shield between the line/ headers, even this will improve.