I had this problem and cured it with some silicone tubing over the fuel line as well as changing the line from copper to steel. Steel doesn't absorb heat like copper.
Here's a "before" pic:
Here's an "after" pic:
Here's the silicone tubing I used. It was 10mm ID and slid over the 3/8" fuel line. 3/8 ID silicone tubing would be too difficult to slide over the fuel line:
https://www.amazon.ca/gp/product/B073DXX9QB/
The steel line was just a piece of brake-line. Cut the flare off one end, cut to length, removed the fittings it came with, installed my own and the tubing, then re-flared the cut end.
Problem gone and has never come back.