How Do You Combat Hot Fuel?

[davis95]

My car runs great before it gets real hot, but seems to be vapor-locking after driving for awhile. I've been tuning my secondaries and cut some transfer slots today which allowed me to back way off on the spring with no ill effects. It actually pulled from a dead stop at WOT all the way up through the gears better than it ever has. Perfect transition from primaries to secondaries with no flat spots, sputters, or pops. When  I got back I parked my car for about 30 minutes and got back in it and it was hard to start (pedal to the floor), but it idled and ran fine after starting. I went back to the exact same spot on the road for a duplicate run of 30 minutes ago and it came up fine until the secondaries started coming in when it felt like it was running out of gas for a second or two. Once the secondaries opened it felt normal. Driving normally there is never a problem, outside of the hot starts. It's just the WOT launches that suffer when the engine is hot. I've noticed this the past couple of weeks how my car runs almost perfect on WOT launches before it gets hot, but after getting hot the secondary transition gets a little rough. I'm running a mechanical fuel pump and have a regulator set at 4 pounds. I also have an aluminum multi-layer heat shield under the carb. What should I do to make my engine run as good hot as it does when it's cool?

[omaha]

the only thing I can think of for now (old-timers you know...) is to run a small bypass somewhere befor the fuel inlet of the carb. One trick I heard was to jam a .023 MIG welding tip in a length of 5/16 fuel line and tee off from the pressure side of the fuel pump.

[davis95]

the only thing I can think of for now (old-timers you know...) is to run a small bypass somewhere befor the fuel inlet of the carb. One trick I heard was to jam a .023 MIG welding tip in a length of 5/16 fuel line and tee off from the pressure side of the fuel pump.

Would this serve the same way as having a pump with a return line going back to the tank? Where are you recommending teeing off to?

[Cliff Ruggles]

4 psi is also pretty "low" for fuel pressure.  It may not be enough to keep the carb full at WOT.  Unless it's a pre-1968 carb or one with the early hinge pin location, you can safely run at least 6 psi fuel pressure with the stock float and correct needle/seat assembly.....Cliff

[davis95]

4 psi is also pretty "low" for fuel pressure.  It may not be enough to keep the carb full at WOT.  Unless it's a pre-1968 carb or one with the early hinge pin location, you can safely run at least 6 psi fuel pressure with the stock float and correct needle/seat assembly.....Cliff

I'll try bumping up the pressure a bit, but if it were a low pressure issue wouldn't it act the same way when the engine is cool? When the engine's still cool it runs like a scalded ape at WOT from a dead stop until well over 100 mph. It's a 1977 carb.

[omaha]

  The tee would be somewhat close to the carb inlet, I think the closer the better.  An electric pump would keep the psi up at idle and would help a little. to a certain extent. The bypass helps keep the fuel circulating, thus relieving some of the heat and the percolation.  This method has been used in the past. ther are alot of other things to experiment with.
Thermostats, insulation, airflow, fuel psi, heat blockage plates and even jetting,  and electris fuel pumps.

[davis95]

  The tee would be somewhat close to the carb inlet, I think the closer the better.  An electric pump would keep the psi up at idle and would help a little. to a certain extent. The bypass helps keep the fuel circulating, thus relieving some of the heat and the percolation.  This method has been used in the past. ther are alot of other things to experiment with.
Thermostats, insulation, airflow, fuel psi, heat blockage plates and even jetting,  and electris fuel pumps.

If I tee into the line before the carb where do I run the hose coming from the tee?

[omaha]

The line would run back to the tank. (I know a pain in the A$$).
Im wondering if the choke might have something to do woth the symptoms you are having. When you stomp it cold, is the choke all the way open? (the choke may be "rich-ening" the cold running engine and maybe the engine like this. (I dont know, just a thought @ 3:20 in the morn. 2 much coffee 2 day! LOL!)

[Cliff Ruggles]

I've ran into fuel delivery issues hot engine only back when I ran a mechanical fuel pump.

I suspect that the "pull" the mechanical pump puts on the supply line may lower the pressure some, which would also lower the boiling point of the fuel.

This new fuel boils and evaporates easy. 

ALL problems I was having ceased immediately when I sumped the tank and installed an electric pump behind the tank, and 8AN lines/fittings everyplace.....Cliff

[davis95]

Looks like it's time for me to uprade to an electric pump. I hear alot of people talking about the 6 psi Carter unit. Where's the best place to get one of these?