boiling fuel

[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.

[danc30]

Originally Posted by 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.

What is that insulation wrap and where did you get it?

[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.

[MrMagoo]

Thanks Sal. I didn't know about the new needles and seats. Is there an optimal pressure? is 8 better than 6.5 on a carb that can handle it?

I'm going to dig out that book, I don't want to misquote it, but I believe the author was stating that there is positive atmospheric pressure in the world inside the air filter created by the air rushing down into the manifold. Something about the Venturi Effect.

[Power Surge]

Originally Posted by MrMagoo

Thanks Sal. I didn't know about the new needles and seats. Is there an optimal pressure? is 8 better than 6.5 on a carb that can handle it?

I'm going to dig out that book, I don't want to misquote it, but I believe the author was stating that there is positive atmospheric pressure in the world inside the air filter created by the air rushing down into the manifold. Something about the Venturi Effect.

It's dependant on your needs. Most street driven carbed cars don't need 8 psi, but it's also not going to hurt anything as long as it doesn't blow the floats open. I run 4-5 psi on my car, but I'm also not making 600hp either.

One thing to keep in mind, is that bowl level height and fuel pressure changes will affect your tuning.

As for the pressure thing, positive pressure does occur, but that's down in the venturi by the boosters, and doesn't have anything to do with the vent tubes up top.

[MrMagoo]

Thanks WTM, that saves me a lot of work, I was just thinking how little I feel like changing all of the hoses.

Sal, others who are interested:

Here were my sources for fuel bowl venting: "Holley Carburetor Handbook" by Mike Urich, page 7:

All bowls are vented to the carburetor air horn to maintain a constant "reference" pressure. This keeps airflow variations - like a dirty air filter - from upsetting the mixture.

Also this, from "Holley Carburetors, Manifolds and Fuel Injection" by Mike Urich and Bill Fisher, page 25:

Because the fuel bowl is maintained at near atmospheric pressure by the vent system, fuel flows through the main jet and into the low-pressure or vacuum area in the venturi.

[Power Surge]

Originally Posted by MrMagoo

Also this, from "Holley Carburetors, Manifolds and Fuel Injection" by Mike Urich and Bill Fisher, page 25:

Because the fuel bowl is maintained at near atmospheric pressure by the vent system, fuel flows through the main jet and into the low-pressure or vacuum area in the venturi.

Yeah, that's the main principal behind a venturi style carb. The venturi creates a low pressure point in the bore, and the booster accellerates the signal. Fuel is drawn into the bore from vacuum on one side, and "pushed" from the other side by atmospheric pressure.

I guess I misunderstood what you were responding to, I thought you meant that the vents could compensate for a mismatch in fuel pressure between the bowls.

[Michael C Henry]

I bought a heatsheild sleaveing product made by DEI from Summit. I covered my BG fuel log and tubes to carbs with it.

[Naumoff]

Decooney,

I didn't go back and reread the whole thread but did you check your timing.
I remember having this issue years ago and it was that the timing to far advanced.