Sometimes on a hot day when I’m drifting (!) around corners, I smell fuel coming out of the top of the SU overflow tubes. A suggestion here is what I’m working on is to add a foot of FUEL hose to each metal downspout and use cable ties to hold things secure. I have to gently use a tubing bender to make a better fit than the factory did with both tubes culminating together on the side of the oil filter housing. Make sure the hoses are extremely tight to avoid losing them on a burnout! BTW I’m still messing with the brake booster problem. It’s 100 F and I’m just not up for that scorching heat without A/C
I do not quite see how fuel can come out of the overflow tubes where they connect to the float bowl cover if they have the proper sealing washers fitted. Are you sure the smell is not fuel boiling out of the two holes in the top of the hisser? These are open to the atmosphere and in very hot conditions (especially after hot shut down) there can be a fuel smell from the engine bay. But worth checking your float bowl lever adjustments.
Or are the float levels too high?
Only time fuel would come out , is if there is a fault , you need to fix the fault , ie too much fuel in the bowl , fitting longer pipes is not fixing the problem .
I did have fuel coming out my old HD6 carbs, but that was coursed by sticking float needle valves , if car had sat a few weeks , had to tap the top of the bowls with a spanner to free them , I joined the 2 pipes together with hose then placed the end of the hose in a plastic bottle , to save it sitting on the floor under the car .
This has never happed on my HS8 Carbs !
Or a bit of fuel in one of the floats will do it, even if the float level is set right.
I’ll check them once I get the brakes sorted. They are neophrene style.