When I am close to having the carbs flood due to heat, (e.g. by time, I know it's getting hot in there) and I suddenly clear the traffic jam thus allowing air into the bay and moving again, the problem doesn't arise at all. Which to me suggests a couple possibilities. Likely it's not the heat shield acting like a heater (cause it would not cool that quickly) and the sudden rush of cool air down the carbs cools them quickly. Maybe if the cool air were running through them the whole time they wouldn't overheat.

I'll let you guys know how it works out. Again, your feedback was most helpful, particularly the gas fumes in the cowl issue.

B

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Webers should be ran at 3psi or less. What you are describing may be flooding due to fuel pressure.

You heat shields look like they prevent any cooling air from entering or exiting the area around the carbs. You likely have no air circulating around the top of the motor while the car is stationary.

My solution to this problem has been to move to a more rural location....works like a charm.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Great idea, Sandy! I grew up in the country, I'll return someday likely.

I run my Webers at about 4 psi, I could dial it down some more, but there is no problem during operation when moving, its standing still with the hood closed where the issue arises. If I shut off the car, the 4 psi holds steady for a long time, many hours, unless the hood is closed, then it bleeds past the power valve and into the intake due to heat build up from no air movement. I've been shutting off the fuel pump and running the bowls down before shutting her down to avoid this.

Yes, a heat shield is a double edged sword in this case. It shields the carbs from direct radiative heat (notice I ceramic coated my exhaust manifolds, but I chose the worst color as black is highly emmissive, should have used silver or white), but you're correct the heat shield also blocks air circulation. That is why I believe adapting/designing a fan shroud with a diverter to direct some air directly over the top of the heat shield is on my to do list to attack this issue.

Brian

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Directing cooling air at the carbs is a good idea ....make sure you provide a way for the air to exit the engine bay as well.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Sandy,

I was just thinking about that on the way home today. If air is pushed and directed from the radiator and across the carbs it will hit the firewall then be deflected to the right and the left, as it can't go up because the hood is there. So doesn't it have to go down past the starter, shifter linkage, exhaust on one side and past the oil filter etc on the other side? That is, there is really no other place for it to go, unless you cut holes in the inner fenders as some folks do. I guess what I'm saying is, why cut holes? If you can direct air flow just under the hood from front to back, won't it naturally find a place to exit? I suppose there is air flow under the car, down by the tires and under the oil pan. Is that a high pressure system or low? I would think high, but maybe the velocity of that essentially laminar flow creates a partial low pressure (vacuum relative to ambient) and suck the air flow downward and out?

I know the flow across the top of the hood hits the windshield and makes a positive pressure at the cowl (hence cowl induction works well). It seems like if I create decent laminer flow across the carbs, from front to back, after it's deflected off the firewall it should push it's way down and out of the engine bay. Seems logical, but maybe I'm missing something.

Dan, do you have thoughts on this?

Brian

Brian

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Tie some ribbons in that area.....put the car on the hoist with the hood closed and everything idling and see whats happening from below.

Just because it should does not mean it does.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Perhaps you could modify your heat shield with an short lip on the front that slopes downwards. This would direct additional air from the fan across the carbs.

I used my high tech drafting program to create a mock-up


You could look for a thermocouple probe for a handheld volt meter and run some experiments with the car at idle, see what kind of heat we are dealing with.

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'73 Gold Duster - /6

What about an insulated box that encloses the carbs with air inlet and outlet snorkels that has computer fans in each snorkel to suck cold air in and blow hot air out?

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Casually looking for a Clifford hyperpak intake for cheap.

James, that is precisely what I'm thinking about. I was thinking about a sheet of material bolted to the fan shroud that directs air over the carbs as you indicate in your rendering. I think this will work.

Sandy's idea is good, but I don't need a lift. I can mount (securely) my iphone under the hood, on the inner fender, and video tape the air flow with those ribbons as markers.

Also, I am going to do a cold air induction system as well. Perhaps both will do the trick....can't hurt and they sound like relatively easy and fun projects. Also, I'll try an air damn on the bottom of the radiator support to drive more air upwards while driving, perhaps that'll get the temps lower while driving so traffic time is increased.

Reed, your idea would definitely work, but it's more complicated to implement. If the carbs were sheathed in a cool air current there is no way they'd ever overheat.

Still, I think that cool air into the carbs should help considerably. Along with better airflow on the outside, it may do the trick. As I mentioned, clearly my air cleaners are in the worst possible place, they suck in the hot rising air when sitting in traffic.

Also, I'll pull my power valves and inspect them. Perhaps my membranes have ruptured or something. I've heard Holley enthusiasts have this problem, suffer from flooding. There is also the thought of using stronger springs in the power valves so it takes more pressure to force the gas past it. This is run by engine vacuum, perhaps I have plenty to spare as it's a new engine and pulls well (vacuum opens the valve, but when the gas boils it is pressure that pushes them open).

Oh yeah, and there is dialing my fuel pressure regulator down a bit, right.

Thanks so much guys for all your help, I'll provide updates/pics. I do like the Webers, the car runs strong and smooth, good acceleration, fast response, decent gas mileage to boot. I get 23 mpg highway, less than 20 city, but average 19.5 mpg.

Brian

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BTW, James that picture you posted is a good pic to show my comment about the side oriented thermostat housing. You can see how that top radiator hose is blocking airflow to the carbs. I hadn't considered that when I installed it.

I used to have a 90 degree gooseneck housing (I took a stock upward aiming slant six thermostat housing, made a 45 degree cut, spun one piece 180 degrees and welded it back together, shown in these earlier pictures:

http://s785.photobucket.com/user/67dart ... html?o=234

http://s785.photobucket.com/user/67dart ... html?o=154

http://s785.photobucket.com/user/67dart ... html?o=187


It raises that end of the radiator hose up and out of the way of the air flow. I'm going to reinstall it. As you can also see, the top of the fan is well below the heat shield level, so a dam or diverter as you drew is needed to direct that airflow up and over the heat shield.


Brian

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I used two stock thermostat housings to make that gooseneck one, I made two 45 degree cuts.. One at the very top of one housing and one nearer the bottom of the neck of the other, so when I put the two pieces together I'd have longer leg lengths on the final construct.

b

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That's why an air dam helps.

Create a low pressure area under the front of the car so the air can exit down..

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

...I guess I didn't think of the dual purpose of the air dam. Since it's scooping up air flow and aiming it up and into the radiator, it makes sense that it's creating a partial vacuum below....synergy. so it would promote flow up to underside of hood across top of engine and down around back of engine bay.

Cool.

brian

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So, I replaced my radiator today. I had that shiny aluminum job, but apparently if you don't use some sort of rubber to cushion them, they crack - and no one will fix them. So, I found an old mopar small block V8 radiator, fixed a crack and a hole and I'm back in business. It is double core (the AL one was triple, but overkill).

Anyway, I found that the gooseneck thermostat housing actually put the top hose more in the way of airflow to the carbs than the side one. What I needed as to lower the hose below the carb heat shield's level all the way across. It previously was lower at the thermostat housing but passed higher than the heat shield level in order to make the connection to the upper radiator inlet. So, I simply twisted my 90 degree hose and added a piece of another hose that had a double 90 degree bend in it. Now the top hose is below the height of the heat shield and there is a strong air flow above the heat shield, though it's not channeled/directed well. I still think I'll need that deflector or something, e.g. like James' rendering. Perhaps a sheet of metal bolted to the heat shield that goes toward the fan or something bolted to the fan shroud (home made) with the same purpose.

http://s785.photobucket.com/user/67dart ... 9.jpg.html

FYI,

Brian

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