boiling fuel

[double ugly]

I picked up the Cobra from Modern Auto today after Troy replaced the rear main seal. It was 112 degrees and the car ran well until I got off the freeway and had to sit through some stoplights. The engine was loading up (oil 105C water 100C). I need to insulate the carb from the manifold. A phenolic block would do this. Any idea where to get one? Jeggs? Any other suggestions? The manifold is a sidewinder the carb is a vintage 780 Holley.
John

[jhv48]

Jegs and Summit both have them in a variety of thicknesses.

Stay with phenolic for heat insulation and avoid aluminum.

Also, make sure you have long enough studs to accommodate the increased height. Summit and Jegs both sell the longer studs.

Finally, make sure your fuel lines are kept out of heats way as much as you can too. Also, make sure you have hood room to add the additional inch of space under the carb. Shouldn't cost more than $50 altogether.

[mobilenuke]

I don't want to start a big controversy as this may only pertain to places that get as hot as we do but if you decrease some of the stainless, cut back on engine "bling" this will help it cool better. These shiney items look good but have poor emmisive properties that tend to reflect infrared waves well.
Doesn't help fuel vaporization as much as a spacer would due to heat transmission through the intake manifold.
Wish I could help on a spacer source for you.


Jeff

[1985 CCX]

John

I have been told thata precision made opart will maximize your performance. As phenolic does work a few friends in the know referenced me to the carb king:
http://www.barrygrant.com/bgfuel/default.aspx?page=60
Barry Grant is the tops in the carb biz....Open plenum for high rpm and ported for low range etc.....

Best of luck
Jeff

[double ugly]

I'll check it out.
Thanks, John

[Cobrabill]

Got a return line on the fuel system?

[double ugly]

It has a mech. fuel pump so isnt pressure regulated.
John

[Rick Parker]

DU: Looking at your gallery, the engine is very nicely detailed, however to fight fuel temp: 1. Try using a non metal hose from the pump to the fuel log. 2. Insulate the attachment of the fuel log to the manifold, as it is it otherwise becomes a big heat sink for the fuel. Although it is a SB, they too can suffer from the same heat issues. My headers I (in gallery)radiate an abnormal amount of heat because of their design. I made the fuel log and attached it with non metallic spacers sandwiching the mounting tabs, keeping them about 5/8" above carburetor base plate. Ultimately I did not need a heat spacer for the carb but used a "little thicker" open plenum gasket purchased at NAPA. They also offer a 4 hole (non-open) gasket of the same material it has a wire mesh in the material. You could also put an insulating sleeve on the fuel log which would not be unsightly. Do what it takes.......

PS: Had the fuel in the vehicle been replaced/added recently or was it winterized fuel with additional oxygen that is often blended into winterized fuels?

[IMG][/IMG]

[Danr55]

John, When you say "loading up" do you mean heating up? I've always thought of "loading up" as an more fuel in the carb than the engine can use. Essentially, flooding the engine while it's running. I may have misunderstood what you meant. 100C is only like about 212F which is about the normal running temp for my car..

[double ugly]

Rick, some good points.
Dan, the carb is getting too much gas and flooding.
John

[blykins]

Loading up is different from boiling the fuel.

How do you know it's getting too much gas? Is gas coming out of the vent tubes? Is the idle too rich? Does it smoke on idle?

[double ugly]

When every thing is really warm under the hood the engine seems to load up. I have to floor the go pedal to restart the engine. It then stumbles and finally clears up for a while then repeats. Four or five times over the last 8 miles.
John

[Jerry Clayton]

John

Do you have a splash pan under your manifold???

Is the heat risor passage blocked off??

Have you tried opening the hood a bit to let heat escape??

Ice on the manifold and fuel line help???

[double ugly]

Jerry, I havent tried anything yet. I don't know whats under the manifold but I'll check with the builder. I'm not aware of a heat riser either.
I talked to Troy at Modern Auto this AM and he recommended a wood spacer in lieu of the phenolic because it insulates beter and doesn't warp. It does need to be replaced every few years though. I need to add an insulator to the fuel log as it's bolted directly to the manifold. I have plenty of insulating header wrap and I may try wraping the fuel lines too. I recall that when these beasts were raced in the 60s it was common to see a block of 2x4 keeping the back of the hood open to let air escape.
John

[MrMagoo]

Your oil temp is quite reasonable. I run a smallblock and would consider 100C high for water, but maybe in a big block on a 112 degree day thats not so bad. I have hit that in traffic on hot days here in the northeast.

I did wonder before I got my carb tuned up right about whether heat was a problem for me, so I installed a Holley heatshield, and I wrapped my fuel line from the pump. Yeah, I am using stainless lines all over the place and I agree totally with MobileNuke that that is a source of heat transfer, which is why I wrapped it, along with the fuel log.

I am also wondering (as the others did) if heat really is your problem. Sounds more like a carb adjustment issue. You have a bog, could be an accelerator pump issue, possibly the size of the nozzles being too small and not pumping enough fuel to cover the transition from idle to main circuit. I would do the spacer, maybe the Holley heatshield kit like I got, and wrap up those lines. Then, see if it still happens (my guess is it probably will). Then attack it as a carb adjustment problem.

[double ugly]

The problem didn't exist at "normal" az temps this winter. This was the first drive in summer temps. I have to conclude that it's the high ambient air temps creating the problem

[sideoiler10]

DU: Have you thought about the heat deflectors that Holley makes? Their footprint extends out completely underneath the bowls of the carb to deflect the heat coming off the intake. They are only about 1/4 in. thick, but I am running 2 of them on my 2x4. Jegs carries them.

Insulating carb gasket heat shield # 510-10851 $21.99 (page 92-U)

If you need to trim a little, they are easily trimmed on a bandsaw.

Give it a look! Bob

[Power Surge]

John, your problem does not sound like heat related fuel issues. It sounds more like the ambient temp conditions are requiring a retune on your carb. Either that, or your fuel bowl level is too high or you have a stuck float. It really sounds like you need the carb tuned correctly to me.

FWIW, I have a MR intake, metal turkey pan, Lemans Holley carb, steel fuel log, steel fuel lines, and just about every other poor scenario you could have on a motor and I have no problems with heat related carb issues.

[double ugly]

It ran great at 70-80 degrees and it's going to that climate this summer. I hate to re-jet for these temps when it's going to "normal" temps. I think I'll have it towed to Modern Auto and have a wood plate installed between the carb and manifold and have him check the carb over. He is really good at this stuff.
John

[Jerry Clayton]

John
Are you still mixing race gas with the 91 octane?

Jerry