boiling fuel

[Michael C Henry]

I went another direction. I installed a BG diaphram adjustable fuel log with return to fuel tank. I have fresh cool fuel circulating just a couple of inches from the carb fuel bowls. I went a little too nuts with the electric fuel pumps. Two Carter 100 gal per hour at 15 psi, seperately switched with check valves , Y , and 5/8" supply fuel line, 1/2' return line, fuel pre-strainers, filter, and fuel log pressure set at 6 psi to two Holley 600 CFM carbs.

[double ugly]

I mix 100 LL aviation gas at 25-33 percent. I don't need to since I'm at 10:1 CR and have access to only 91 octane but I like the smell. Reminds me of the old days.
John

[My427stang]

I dont think most of the nation can understand the heat off of the pavement, especially from the desert.

Mine ran great everywhere, until I got stationed at Nellis AFB. I then fought percolation like you, pavement temps of 150+ are something east coasters (like I was) never even considered.

High fuel pressure from pump to as close to the carb helps vapor lock, but you have to keep heat away from the carb because it operates at zero pressure. Ultimately, even a carb heat shield will allow the heat to saturate if you dont have airflow to take the heat away.

Look to have a return line to keep fuel as cool as it can be, at the starting point, insulate lines from ground heat where you can as well, and make sure the carb isnt buried in goodies preventing airflow around the body of the carb. Anything you can do to get airflow AROUND the carb, not just INTO it will help dramatically

In addition, drop base air cleaners act as heat umbrellas, so any way you can run a flat base will help as well to let heat evacuate

Finally, west coast fuel, and 50 state winter fuel will flash off much easier at low PSI and zero psi internal to the fuel bowls, I wouldnt expect AVGAS to have that issue though, so you could always increase your percentage

Ultimately, the real "perfect fix" is EFI, but I bet you can get a lot closer with some heat management

[Michael C Henry]

My dad had a large 1 ton and loaded it up and towed a trailer NEVADA ,Arizona, and New Mexico . He delt with vapor lock and all. His final cure was to add a splash of ATF to raise the flash point.

[MrMagoo]

ATF, hmmm. How about good old MARVEL MYSTERY OIL That is an interesting idea, and one of the many cure all benefits of the MMO explained.

After reading everyone's ideas on heat, I think I may replace a stainless braided hose that goes TO the fuel pump with rubber. Do you think that ambient heat from the road at 150F makes a difference when you have 800F coming from the headers, and an oil temp in the motor of 220F? I'm sure it doesn't help, but I wonder how significant that would be.

[Bxx1]

Facinating link, you guys give me soooo much to think about. The knowledge here is terrific!

[SLHetal]

John,
It might be a stupid question but how are your spark plugs reading? Fuel loaded? Maybe ask your mechanic about plug heat range for your current high ambient temperatures.
Sam

[decooney]

I have a return line, and a Turkey Pan to help cool the float bowls, and when I'd get to a very specific stretch of road between Fernley and Sparks Nevada (every year) mine does the same. Loads up, and runs like the fuel is just boiling in the bowls. Take it out at night and run it around, when it's cooler, and see if it loads up in the same way. Hmmm, vapor lock. Dry / Hot-Heat / Hot pavement / Thin air... same scenario. Over seven years with my car (rarely driven though) this situation only occurred for me in the desert in the exact same spot and stretch of road, 4,300 foot elevation, same time of year and temp, two years in a row and nowhere else near my home - knock on wood. Well, we have a 105 degree day today coming... we'll see.

Good tips from many folks here on this topic... I may end up replacing my braided line from the fuel pump to the carb fuel log next.

[Naumoff]

Sounds like a typical Holley. I agree with Sal. I have Mechanical pump , steel lines, factory fuel filter next to the remote oil filter, steel fuel log, and the heater lines run right next to the fuel log. It can be a scorcher here in So.MD on the bay with no vapor lock issues.

A vintage 780. Did you install the better needle and seats?
Where is your fuel filter located?

[double ugly]

The car goes to Modern Auto next week. I'll ask Troy about the needle and seats. The fuel filter is in the stock location on the left front of the engine. I'll also ask about the return line.
John

[Mike Bartlett]

DU I had the same problem in Reno, what decooney was referring to, with my car. Hot as hell 105+ and high altitiude. My car stalled while in slow moving traffic through Viginia City. Acted as if too much fuel getting into the carb. Got back to The Nugget in Reno and lowered my float bowl level a bit. I went through even hotter temperatures the next day driving home. No problem at all. A quick fix that just took a few minutes.

Another thing a buddy of mine and I checked was front bowl temp after that hot drive. We got back to Reno and with almost identical motors my firends Cobra front bowl was considerably cooler (with Turkey Pan) than mine with no Turkey pan. I think that aluminum really helps keep the bowl cooler. I do have the Phenolic spacer and my fuel log is isolated but obviously it didn't help much. I believe the problem is the fuel gets real hot at times, then with thermal expansion, it forces itself through the needle/seat causing the motor to richen up then flood itself?

The only other observation I made was my fuel pressure at the time was about 8-9 psi. I am not sure what the "norm" or max should be?

Mike

[MrMagoo]

The float bowl pressure should be equalized, that's what those two pipes sticking up out of the air horn are for, they vent to the inside of the air filter, thus keeping the pressure inside the air filter and inside the float bowls equal.

A fuel pressure of 8-9 is WAY too high for a holley. Max should be 6.5. You need a regulator. Are you running a mechanical fuel pump or electrical?

[Mike Bartlett]

My pump is mechanical. Normally it runs around 6-psi but that hot weather it jumped to 8+. I do not have a regulator...yet!

Mike

[jhv48]

My BG does the same thing now that the weather has turned hot.

This is definitely a heat soak problem. I have the stainless wrapped lines, metal fuel filter sitting atop one of the valve covers and a drop base 14 inch air cleaner.

As soon as I get a couple of miles on after hot restart, things cool down and it runs normally. But after sitting in the sun, restart acts like it is loading up.

I adjusted the floats down a bit and wrapped the fuel filter to insulate it. Problem got better. Now I will try another air cleaner and see if that helps. Spacer is next along with rubber fuel lines.

[Rick Parker]

If you are running meatal lines from the mechanical pump to the carb, the heat soak problem will become greater as the line conducts heat from the mechanical pump. It is best to change to a rubber lined hose.

[MrMagoo]

If heat is causing your fuel pressure to rise to 8-9, then that could be a huge part of your problem, since Holley's are very particular about excess fuel pressure above 6.5. Before you get a regulator, do all of the cooling suggestions first, and see if you can prevent that from happening. That way, you will know if the cooling you are doing is effective.

[Gaz64]

The fuel in the log is "boiling" because of the combination of three things:
high ambient temp, engine bay temp, and slow fuel flow because there is less fuel flow through the secondary fuel bowl than the primary.
The secondary idle circuit is not supplying the motor as much as the primary.
So, how about feeding the fuel log from the rear, or fit an electric pump with a bypass regulator and you'll always have cool fresh fuel at the inlets.

[MrMagoo]

I agree that an electric fuel pump is better as far as heat transfer is concerned, but I switched to a mechanical for several reasons. I hate the whine. At a stop, its nice to hear just engine sounds. Electric pumps don't like being put away for 6 months in the winter (as we do here in Connecticut) amid frequent changes in humdity and temperature. The mechanical is nice in that if the engine fails in an emergency, you don't need to remember to flip the cutoff switch or the ignition off. You don't need a regulator. Less strain on the battery in trafffic. They are very sensitive to voltage fluctuations. One less thing to worry about. And finally, the last reason, an appeal to authority! The gruff and lovable Joe Lapine of Danbury Competition Engines hates electric fuel pumps on street cars.

On the whole, unless I was racing or running fuel injection, I prefer to stick with the mechanical, and do everything else to eliminate heat transfer.

If your sole goal is eliminating heat in the fuel, a system with an electric pump and a return line like you would use in fuel injection is probably ideal.

I don't know about reversing the fuel lines and feeding from the rear. It's an interesting idea and you've probably found that it works, but the conventional wisdom has you looping your fuel line in the front to the carb, with acceleration pushing fuel towards the carb instead of away from it. This may be a case of engineering trade offs, and in a hot place, it may be that the benefits of secondary first feeding outweigh the negatives.

[decooney]

After reading through this thread, and great replies, I'm thinking about trying to cover and wrap my braided line setup from my fuel pump to my carb before scrapping it. Or, maybe just reroute the lines all together from the rear instead, which also seems like an excellent alternative.

A friend has the same setup that I have in his 390GT Mustang and was experiencing horrible fuel boiling. So, he actually took this stuff below and covered his lines with it. I've used it for my clutch hydraulic clutch lines too. Since it looked kind of ugly, he then wrapped it with that special black felt type electrical tape to make it look less noticeable. He says he does not have the boiling fuel problems any more. His engine bay gets as hot or worse than our Cobras and experiences the same hot start issues when it's just sitting in the sun on black pavement.

[MrMagoo]

I wrapped my line from the pump to the carb, added a holley heat shield with spacer, laid a piece of reflective insulating pad underneath the fuel log and just generally tried to eliminate obvious points of heat transfer. I like the results. The car doesn't get doggy when it's hot like it used to.

I'm seriously considering getting rid of the braided steel lines for fuel entirely and going with rubber and insulation, but no urgency at this point.