Fuel system with return line.

I have this exact same problem, and it started as soon as the winter blend gas went away. It is aggravating as all heck!! Mine only percolates in the rear bowl though. The front must move enough fuel during cruise to keep it from happening.

As soon as I try to make a WOT Run, it eats all the front bowl, and gets to the back and just sorta shuts off. I can see the gas boiling through the sight glass.

I am also looking at building a return style system to cure it.

I first ran into this problem a couple years ago. Driving home from work (65 mph on the highway mostly) I stopped at the gas station, then the car was a bear to refire. Flooding out, would run briefly then die, blah blah blah. Had that happen a couple of times after that before I broke down and spent the money on a bigger pump, regulator, lines, etc. It was definitely worth the money.

Only time I've had an issue w/ it recently was during the True Street race at Rockingham a few weeks ago. We had to do a 10 mile drive, then pull into the lanes w/ NO cool down time and do 3 back to back hot laps down the 1/4 mile. I didn't have enough fuel in the tank so it started recirculating hot fuel...it used more than I anticipated. By my last pass it almost died coming out the water box from the fuel being so hot and trying to vapor-lock. It ran 3 dead on 10.01 at 135 mph passes w/ a broken torque converter and won the class, so I wasn't too upset, lol.

FWIW
I run a mechanical pump and factory style vapor separator with a return line. I have driven my cars all over the country in very extreme conditions and with all different kinds of gas. My car's fuel system is quiet, stock and dead reliable and would be easy to get parts for anywhere.
I don't need all that fancy racing stuff on my street car. How many of you can say you've driven your car at near wide open throttle for miles at a time, like over 5 miles at a time in 95 degree weather at 6000 feet alitutde? It never ran out of gas. I also drove it in 115 degree temps in Vegas last summer with the AC running the whole time.

I don't need no stinking vapor locking electric fuel pump on my street driven muscle car.

My carbs is bolted right to the intake manifold with no spacer/bandaid.

I ran a wood spacer on my 340 to stop percolation, it sounded like a coffee pot a few minutes after I shut it off.

When I built the 408 I ran a 1/2" line up the inside of the frame rail to the regulator (non return)from the Holley billet black pump. In real hot weather the car would do the same thing as Rons, it would boil the gas and flood going down the highway. My car has air pans sealing up the front and the carb was sealed to the hood so pretty much the only air going through the engine bay came through the radiator. I fabricated a shield for the line where it passed by the header and removed the air pan sealing the hood but it would still do it in very hot weather.

The fix for me was to route the fuel line over the frame tie behind the trans crossmember, through the inner fender into the wheelwell on the passengers side and through a bulkhead fitting in the front of the inner fender to the regulator mounted there. I also replaced the 3/8" line from the regulator to the carb with 8AN. No issues since, my heat was coming form the headers and the lack of airflow in the engine bay compounded the problem. BYW I'm still using the Holley deadhead regulator.

I understand that a electric pump can work fine on the street. The problem I see with performance pumps is that the suction line usually is not big enough expecially with a stock tank. Lot's of guys struggle with electric fuel pumps because of the suction side is not big enough for all conditions.imo

Yes the key is circulation to keep the fuel cooler.

Yup spacers can and do help alot, but my point is. Properly setup and tuned they are not needed, imo.

I guess this thread isn't about a fuel delivery issue as much as it as about a fuel temp issue - although they can be some what related. Funny how this topic often pops up around this time of the year when stations are switching over from winter ( 14-16 RVP ) to sommer ( 8 - 10 RVP ) - expressed in PSI - blend. BTW, race gas is usually in the 5-7 RVP range, so not a problem. Cold climate areas also are the most effected as the change over has the biggest RVP swing. There aint no real good solutions for your high powered street machine, but here are some that may help. As said, a fuel return line system will help a little ( not for pre-soak issues though ). Dump your existing winter gas ( if your car has sat for a while ) and put it in the grocery getter ). Fill up from a station that is always busy - best chance to get summer fuel. Run a carb insulator type spacer. Lose those pretty stainless jacketed fuel lines and replace them with ANYTHING not covered with a steel braided jacket. Run the lines / regulator as far away from the engine as possible. Get the heat out of the engine bay. Run electric fans for a few minutes after shutdown - like at the gas pump while you are filling up or - raise the hood. Remove the inner fenderwell splash guards. Raise up the back of the hood an inch or two ( ala old school ). Run a 160 stat - if your system can stay on it - or no stat. Insulate your headers - and fuel lines. BTW, the fuel in the old Thermoquad ran about 10-15 degrees cooler with their plastic fuel bowls ( guess this problem has been around for a while ). Looks like the new Demon street carbs are trying to address it also. IMO, the biggest problem is heat trapped in the engine bay. What ever you can do to reduce it will be the biggest help in solving this problem.

I run a 1" plastic spacer and even put a heat shield under the carb to see if it helps. It only seems to do it after its hot and shut down for a few minutes you know a hot soak. Thats when it seems to happen. Never had any problems last year or ever before. Ron

Under extended WOT high speed conditions there is usually plenty of airflow in the engine bay and lots of fuel consumption keeping everything reasonably cool.

In other words, the exact opposite of what causes the issue