Heat soak? Edelbrock carb & air gap

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19blockhead72 said:
Mechanical, I think 160 gph 6psi.
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well, as I expected, the question has been kicked around pretty well and answered with several excellent suggestions - I agree that putting in an electric fuel pump will help immensely, which was where I was going with my question a few hours ago
 
ScampMike said:
well, as I expected, the question has been kicked around pretty well and answered with several excellent suggestions - I agree that putting in an electric fuel pump will help immensely, which was where I was going with my question a few hours ago
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So electric pump because mechanical gets hot? Just wondering the reasons.
 
Electric pump because it is constant & immediate for bowl filling.
 
yep - more consistent and constant pressure than a mechanical pump can deliver - under any conditions
 
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rumblefish360 said:
Electric pump because it is constant & immediate for bowl filling.
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Well I considered an electric pump at the beginning of my build but ended up just keeping it simple by going with the mechanical pump. Guess maybe I'll revisit this hole fuel pump thing and change it up. Thanks for the suggestions.
 
Fuckin A Mike!

To the OP, I made a mention to a return line. If your car has one, make use of it. It helps keep the pump cool under less stress (& longer life because of
It) and the fuel in the line cooler.
 
Same thing here with my swinger. 3/8 copper nickel/ 1/4 return line, mech pump, performer intake with cerekote thermal barrier coating underneath,TQ with thick gasket,and functional dual scoops. I tried the good NASCAR insulation with no help. The weird part is if I fire it back up within 15 minutes I'm fine. Or if I wait 2 hrs its OK. Also tried the old clothes pin trick to no avail. Tried lifting the hood right away. Before I had the return line I put a clear filter on it, just to see into the fuel system. After 5-10 minutes it would start getting bubbles in the filter coming from the carb side. So that's when I chalked it up to the bullshit fuel, and am saving up for the aeromotive/tanks inc. Setup. Also like to mention when it happens I have to crank it for 20 seconds to get it to start, and when it does it blows rich from the pipes.
 
Well, guess the reason it blows rich is because it seems to start faster if I hold it on the floor. Also I forgot that it did it just the same on a 50/50 mix with pump 93 and 100LL av gas.
 
Dana said:
Same thing here with my swinger. 3/8 copper nickel/ 1/4 return line, mech pump, performer intake with cerekote thermal barrier coating underneath,TQ with thick gasket,and functional dual scoops. I tried the good NASCAR insulation with no help. The weird part is if I fire it back up within 15 minutes I'm fine. Or if I wait 2 hrs its OK. Also tried the old clothes pin trick to no avail. Tried lifting the hood right away. Before I had the return line I put a clear filter on it, just to see into the fuel system. After 5-10 minutes it would start getting bubbles in the filter coming from the carb side. So that's when I chalked it up to the bullshit fuel, and am saving up for the aeromotive/tanks inc. Setup. Also like to mention when it happens I have to crank it for 20 seconds to get it to start, and when it does it blows rich from the pipes.
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How does air flow down hill from the carb to the filter?
It doesn't!
The fuel is boiling.
Why?
Because the float valves have dropped, the pressure has been released, and hot fuel boils rather easily. The fuel is boiling everywhere there is a hot spot between the carb and the pump.
What to do?
Eliminate the float drop.
How?
Well yeah that's the tough one. The fuel is leaving the bowls. It may be evaporating, boiling, or leaking.
There are three ways for heat to get into that carb; namely; conduction,convection,and radiation. Conduction is by being in contact with other hot parts. Convection is by contact with trapped hot air circulating under the hood. Radiation is just by being near other hot parts. Hot always travels to cold
Your first line of defense is to make the carb,and/or the fuel stay cooler.That is tough when it is baking in the underhood oven.Insulators and aluminum plates get hot in that oven too.
I removed the hood insulation, allowing that hood to become a giant heat sink on the bottomside, and a giant radiator on the topside.
I cut several holes in my hood to allow the heat to escape.
I cut another big hole in my hood for topside air to fall into the carb. Now this colder air picks up heat and rises out of that chimney, to be replaced with cooler air. This is convection.When it leaves, it may take some fuel vapors with it. So even if my fuel was to boil and enter the throttle bores, it would rise up and out of the chimney rather than run down inside and flood the engine.
These are some of my tricks. You may not wish to cut holes in your hood, which is why I suggested to take it off for a week or so.
Also, I have a high-powered cooling system. It runs at a constant 205*F. None of this electric BS where it might run up to 215/220, and then the fans kick in and drop it down to 195, in and endless loop. It runs at a constant 205*F.So,when I shut it off, the water is at 205. With an electric system, it may be at minus 1* from triggering the relay, say at 214/219, lol. I hope you don't have an electric cooling fan system, cuz fuel boils sooner and faster with higher underhood temps,lol.

Now, having blathered on and on, What if just one of your float levels was just low, or just one of those valves was not able to stay closed against your pumps pressure.
Your second line of defense is maintaining the pressure in the line. As soon as the pressure drops,just a little, the fuel will want to boil. In fact gas can want to boil at 100*F. Some components will boil at waaay less temperature. If they didn't, you would never be able to start your car in winter. So put a pressure gauge on it and see what is happening. I bet your trouble starts as soon as the pressure drops to zero. or shortly thereabouts.
So what is happening? Is the pressure dropping cuz the float-valves are bad? or is it cuz the fuel level in the bowl dropped far enough to allow the valves to open.
I cannot say.
It could even be a bad pump allowing the fuel to migrate back towards the tank. Or a small leak at any jumper-hose.Either will show up as a drop in pressure on the gauge.
You will have to be the detective.
While you are watching the gauge, keep an eye on the carbs bowl vent, and also on the throttle blades, and the boosters; looking for liquid fuel, or the tell-tale shimmer of the evaporating fuel.
Bon chance,mon ami
 
AJ/FormS said:
I don't get it
I have a Holley 750DP on my 360 on top of an AG. I run un-wrapped TTIs and aluminum heads . The water temp is a minimum of 205. I run the HO Carter pump with a 3/8 steel supply line, all the way into the tank. I run 87E10 exclusively.
I never ever have these kinds of problems.Not on the hottest days of summer nor under any kind of operation. Mind you we rarely see more than about 100 degrees in the shade.
I think I will get me an Edelbrock just to see what all the hullabaloo is about.
My answer is borrow a Holley, see what happens. Holleys have the bowls hanging out in the wind. And a great accelerator pump system.

As for me, I would not be looking at the fuel delivery system nor to the fuel. And with the AG, I find it difficult to think it might be hot-fuel.
But to prove it either take the hood off for a tankful, or pop the hood every time you park it. Time will tell.

Here is another thought; perhaps your engine is creating more heat than it needs to. Late timing will lead to the A/F charge not finishing it's burn in the cylinder. Then it may continue in the headers. The headers have no water jackets, so the heat goes into it's surroundings. I big cam will do the same.
If your engine is sucking hot underhood air, what would you expect. Take the hood off for a tankful.
Now here is the biggie;
If your supply line is within a few inches of a header pipe, move it! I put mine inside the frame all the way to the pump. I strapped my engine down and ran a really short rubber jumper across the gap. Insulation does very little when nothing is moving; it gets hot like everything else. Hot gas can flash to vapor as soon as it drops into the bowl. The sudden pressure change causes it to boil instantly.
Click to expand...
I did the same, ran the gas line thru the frame and frame connectors all the way back, and came out a hole right by the pump, located behind the tank. only had to elongated the hole a little .
 
A/J Thanks pal, And I agree the bubbles were there because room was MADE in the carb! Boiling was the first issue i adressed. I have no hood ins. and have two 5 inch holes underneath the twin scoops. And the 50/50 av gas mix was conservative. I've had as much as 11 gallons of it in at once. I don't think that stuff boils very easily. So on to leakage; Started out with the $100 carter mech pump. It put a hole in itself after about 200 miles. Got a $20 cheapy now. Scott Smith did a meticulous job on this TQ, and i hated to question his work. But i went in and verified float levels and everything else was in order. Three things are on my mind at this point. These Tq's were invented to because of the BS fuel. They are said to drop bowl temps by 15* and the stock gasket is 5/16 thick paper! But I'd like to try a thicker insulator. #2 Because of the frame connectors, I have two 90*'s in my fuel line. For some reason cavitation keeps popping in my head? What do you think? #3 At idle if i take my breather off and stick my hand over the 1 1/4 hole in the valve cover, it quickly starts to create a pretty strong vacuum. Its pretty loud when I remove my hand after 10 seconds. So if the pcv closes after shutting the engine off?? Could it draw from the carb?? I'm down to abstract thought here!
 
Well, those are some tuff questions.

But I guess the first question that shoulda been asked was " What fuel are you using?" And the second shoulda been, Why in the dickens are you running anything but pump gas in a "mild 408", on the street? So that wouldda lead to a third question; "what ,to you, is a mild 408?" You said Edelbrock carb in your title. A TQ is not normally called an Edelbrock. That now begs a Fourth question; what Edelbrock carb do you have?

Here is something you might already know
Can I run AvGas in my vehicle?
LL100 has the same flashpoint as gasoline namely -38C,. That's minus 38C, minus 36.4 F . The flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air.

#1, CARTER ThermoQuads are, in my mind, the greatest street carb ever invented.
#2, A pair of 90s in a 5/16 line is very bad for a 408. A pair of 90s in a 1/2 in line, on the street would be no big deal for a rear mounted pusher-pump.IMO, on the street your 408 will be fine with a pair of 1/2inch 90s, and a sucker pump, although I wouldn't have set it up like that.I would not run two of 3/8 90s even on my 367, with a sucker pump. But these 90s have nothing to do the issue of this thread.
#3, When the engine quits, the vacuum collapses, and besides, with the breather back in the hole, I doubt you could measure a vacuum there at all.
#4, When you said Edelbrock, in my mind,I saw AFB/AVS,all aluminum carbs.
 
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I'm using a mechanical fuel pump with a Performer manifold, which I think vapor locks even worse than an Air Gap does. I solved my hot start problem completely by using a product like Thermo Tec Thermoshield insulation tube around the fuel line, and installed thick nylon washers or bushings between the line and the block where the line is bolted to the block.
 
Mechanical fuel pumps seem to have these hot start problems. A diaphragm with vapor in it just doesn't like to pump fuel uphill. Cavitation in a mech pump isn't a problem, but the phenomenon associated with what happens during cavitation can occur. Say the mech pump itself is full of vapor after sitting, you start the engine, it attempts to pump. It won't pump vapor, but it will lower the vapors pressure inside the line back to the tank. Lowering pressure will lower the boiling point, creating more vapor in a vicious cycle. This is rare but can happen, it must have vapor pockets between tank and pump, usually created by fuel lines close to headers. This is so neat because you can actually boil water at room temp if you put it in full vacuum.
 
So how does adding a return line help, since taking away pressure lowers boiling temp?
 
Dana said:
So how does adding a return line help, since taking away pressure lowers boiling temp?
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Go back to post #22, Notice how the fuel filter is oriented with the nipple up. Any air or fuel vapor in the line,will take the path of least resistance, and scramble up that nipple as fast as it can. And it will be driven back to the tank by liquid fuel following. When you shut the engine off, and the pressure relaxes, then any fuel boiling between the pump and the filter, will send the vapors out the return line.While there may or may not be vaporous gas in the short tube from the filter to the carb, this is easily dealt with. Further more as the fuel cools in the line, it will condense back into a liquid state.The mechanical pump will fill the remaining portion of the line in a few engine revolutions.
The vaporous fuel in the return line will very likely have condensed back to a liquid state by the time it gets back to the tank.If not, vapor pressure in the tank will force it to
Air will escape via the venting system.
 
Seem like post 22 is a catch 22! It encourages a pressure drop then tries to get rid of vapors. My 85 D250 came factory with one of them filters, but also has an auxillary pump at the end of the pickup and a mech pump. Another thing this TQ has a base plate of an 84' 360. But vents to the atmosphere like a 71' TQ. And AFB or AVS.
 
Well the orifice in that return nipple is very small. Most mechanical pumps can deliver 2 or 3 times more fuel than what your typical SBM can use on the street. That little orifice ain't no big thang.
 
AJ/FormS said:
I don't get it
I have a Holley 750DP on my 360 on top of an AG. I run un-wrapped TTIs and aluminum heads . The water temp is a minimum of 205. I run the HO Carter pump with a 3/8 steel supply line, all the way into the tank. I run 87E10 exclusively.
I never ever have these kinds of problems.Not on the hottest days of summer nor under any kind of operation. Mind you we rarely see more than about 100 degrees in the shade.
I think I will get me an Edelbrock just to see what all the hullabaloo is about.
My answer is borrow a Holley, see what happens. Holleys have the bowls hanging out in the wind. And a great accelerator pump system.

As for me, I would not be looking at the fuel delivery system nor to the fuel. And with the AG, I find it difficult to think it might be hot-fuel.
But to prove it either take the hood off for a tankful, or pop the hood every time you park it. Time will tell.

Here is another thought; perhaps your engine is creating more heat than it needs to. Late timing will lead to the A/F charge not finishing it's burn in the cylinder. Then it may continue in the headers. The headers have no water jackets, so the heat goes into it's surroundings. I big cam will do the same.
If your engine is sucking hot underhood air, what would you expect. Take the hood off for a tankful.
Now here is the biggie;
If your supply line is within a few inches of a header pipe, move it! I put mine inside the frame all the way to the pump. I strapped my engine down and ran a really short rubber jumper across the gap. Insulation does very little when nothing is moving; it gets hot like everything else. Hot gas can flash to vapor as soon as it drops into the bowl. The sudden pressure change causes it to boil instantly.
Click to expand...
Maybe it's the blend of fuel. I'm not sure what hippie juice they serve here in tree hugging California, but it isn't the stuff they had in the 70s.
 
AJ/FormS said:
Well, those are some tuff questions.

But I guess the first question that shoulda been asked was " What fuel are you using?" And the second shoulda been, Why in the dickens are you running anything but pump gas in a "mild 408", on the street? So that wouldda lead to a third question; "what ,to you, is a mild 408?" You said Edelbrock carb in your title. A TQ is not normally called an Edelbrock. That now begs a Fourth question; what Edelbrock carb do you have?

Here is something you might already know
Can I run AvGas in my vehicle?
LL100 has the same flashpoint as gasoline namely -38C,. That's minus 38C, minus 36.4 F . The flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air.

#1, CARTER ThermoQuads are, in my mind, the greatest street carb ever invented.
#2, A pair of 90s in a 5/16 line is very bad for a 408. A pair of 90s in a 1/2 in line, on the street would be no big deal for a rear mounted pusher-pump.IMO, on the street your 408 will be fine with a pair of 1/2inch 90s, and a sucker pump, although I wouldn't have set it up like that.I would not run two of 3/8 90s even on my 367, with a sucker pump. But these 90s have nothing to do the issue of this thread.
#3, When the engine quits, the vacuum collapses, and besides, with the breather back in the hole, I doubt you could measure a vacuum there at all.
#4, When you said Edelbrock, in my mind,I saw AFB/AVS,all aluminum carbs.
Click to expand...

Dana said:
You're getting me and the OP confused.
Click to expand...
 
Here is a fello with no problems;
71DodgeDemon340 said:
Running 93 octane, just a regular rpm performer intake, stock hi po manifolds. Run 180 in winter and maybe 190 in summer with stop and go, have dual functioning scoops with the open spots on the air cleaner. Also have heat sleeve on the fuel line from about half the car all the way up to the carb as well as a heat shield on the pass rear where the exhaust is closest to the fuel line
Click to expand...
In fact he hadn't even thought of percolation.
So there may be a possible recipe for you
 
thanks for putting me on the spot lol, i have heard of vapor lock of sorts, i did notice it some, mainly on restart, but actually since i have put the heat shield on the rear covering the fuel line on the frame rail near the exhaust it seems to be gone, we will find out this summer, never had issues once it was running though, seems like i had to give it a little extra gas when starting with it hot out
 
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