The carb base DOES serve a purpose!

[page62]

I took my '62 Ranchero out for a drive in the 90+ degree heat on Saturday. (Yes, it got very hot down here this weekend!) Got stuck in downtown traffic. Every stoplight was red. Well, the engine got hot. And after a while, it started bogging badly when pulling away from a stop.

So I checked with my local guru (who REALLY knows his stuff). He said the gas in the float bowl was percolating due to the high heat. The solution is to hook up the heater hoses to the coolant passage in the carb base. According to him, a LOT of folks (like me) bypass the coolant passage and then try to chase down all sorts of carb-related problems around when in fact the solution is amazingly simple.

Apparently, the coolant passage not only warms up the carb in the winter but it also keeps it from getting too hot in summer. The carb suffers massive heat soak because the exhaust manifold is directly below (and bolts into) the intake manifold.

And remember, down here we don't call that green stuff in the radiator "antifreeze", we call it "coolant".

 

[CobraSix]

In theory, yes.

Here is where I don't follow it. On a nice hot day, your engine is running at 196* (Assuming you have the stock T-stat). That means your carb base plate will be 196*, right? gasoline start baking off at well below 196* so I personally wouldn't want the carb sitting on top of a 196* hot plate.

Sure, it may pull some of the heat from the exhaust out, but that little of a surface area will make hardly any different.

Just my 2 cents.

 

[Bort62]

I would really have to do some testing, but IMO slade is right.

I've never run one, and never had a problem w/ fuel boiling the bowl.

 

[fordconvert]

I dont remember where that is in the flow. If its 'cold' coolant from the rad before it goes through the motor I could see it being a real help because it could then be 150* vs the 240 that would be on the way out. If it was on the hot side it may make things worse.

Anybody see a recent chart of the boiling point of 'modern' fuels? I know the blends are lower by just enough to cause serious issues in all my older cars.

 

[Bort62]

It's on the hot side.

I should add that I lived in the Mojave desert for a year, and didn't have any problems It got pretty hot...

But, no matter how hot it got - it was still cooler than my coolant

 

[jamyers]

Is this your old carb or the one I sent you?

I had the same issue with the Autolite 1100 I just sent you, the solution was to get really picky about setting the float height, and I lowered it to 1 5/16" (iirc).

 

[page62]

Is this your old carb or the one I sent you?

I had the same issue with the Autolite 1100 I just sent you, the solution was to get really picky about setting the float height, and I lowered it to 1 5/16" (iirc).

Actually, your carb was worse than mine! When I got home, I installed it as a test because I knew you'd set the float height. I only got about one block before it started doing the same thing. So I went back to my original carb and hooked up the cooling system. So far so good. It also seems to help the carb get up to operating temp more quickly.

In any case, I'll keep y'all posted on how this works out...

 

[MustangSix]

In theory, yes.

Here is where I don't follow it. On a nice hot day, your engine is running at 196* (Assuming you have the stock T-stat). That means your carb base plate will be 196*, right? gasoline start baking off at well below 196* so I personally wouldn't want the carb sitting on top of a 196* hot plate.

Sure, it may pull some of the heat from the exhaust out, but that little of a surface area will make hardly any different.

Just my 2 cents.

It does make a difference, especially on a stock engine without a port divider. Keep in mind that the roof of the center two ports are actually the floor of the intake right below the carb. Your engine may be running at the temp of the coolant, but localized heating could raise the temp of the carb to much higher than that.

 

[james singleton]

Page62, You wrote the following: "Apparently, the coolant passage not only warms up the carb in the winter, BUT IT KEEPS IT FROM GETTING TOO HOT IN SUMMER".

Maybe somebody will enlighten me here. I can see where in the winter months when you start the engine and the thermostat is closed, that this would help heat the carb spacer/carb heat up quicker; but I don't quite follow the logic of this helping to keep the carb spacer/carb to run cooler during the hotter summer months?? It would seem to me that once your thermostat is open (during the summer) that the temperature of the coolant going through the carb spacer would be the same as the temperature of the coolant that is passing through the engine block. Somebody please explain. Thanks! Jim

 

[Anlushac11]

8)

Seems to me that you could fashion a aluminum heat shield to deflect heat away and use a thermal resistant material to mount the carb on so it doesnt soak up heat from the intake.

That way fuel stays cool but intake stays hot so the gasoline will vaporize and mix with the air more evenly.

Just my .02c

 

[Bort62]

Well, the theory (and Jack's point) is that the flow of hot exhaust gasses causes some localized heating @ the carb mount flange, and henceforth the carburetor itself.

It's true that the center exhaust ports share a wall with the bottom of the intake manifold, and there is no coolant passage in the near vicinity.

So it makes sense that the area would and could get significantly hotter than the coolant or the block as a whole.

So, take that for what it's worth. Some seem to have problems, and others do not. I think that using the carb spacer is probably a good idea on a stock or near stock application. However, I wouldnt stress about not using it, either. I've never had one on mine, and never experienced the problems supposedly associated with it.

Maybe one of these days I will get bored, and throw a few thermocouples on my carburetor. Then we can get some real data on this.

 

[CobraSix]

In theory, yes.

Here is where I don't follow it. On a nice hot day, your engine is running at 196* (Assuming you have the stock T-stat). That means your carb base plate will be 196*, right? gasoline start baking off at well below 196* so I personally wouldn't want the carb sitting on top of a 196* hot plate.

Sure, it may pull some of the heat from the exhaust out, but that little of a surface area will make hardly any different.

Just my 2 cents.

It does make a difference, especially on a stock engine without a port divider. Keep in mind that the roof of the center two ports are actually the floor of the intake right below the carb. Your engine may be running at the temp of the coolant, but localized heating could raise the temp of the carb to much higher than that.

I understand that, but the actual application of it seems to be insignificant. Just not enought surface area for that coolant to really do any noticable cooling of the carb base. Remember, you could have 40* cooler water running through there, but without enough surface area, it won't make a lick of difference. On a cold day, which it is designed to be used, warming up to 196* compared to a 30* winter day, that's a 160* difference that makes up for lack of surface area.

 

[page62]

I understand that, but the actual application of it seems to be insignificant. Just not enought surface area for that coolant to really do any noticable cooling of the carb base. Remember, you could have 40* cooler water running through there, but without enough surface area, it won't make a lick of difference. On a cold day, which it is designed to be used, warming up to 196* compared to a 30* winter day, that's a 160* difference that makes up for lack of surface area.

If the carb base can quickly raise temperatures, it can cool things down, too. Think of it as a temperature moderation device. It's made out of aluminum (or an alloy), which would have a higher heat absorption and dissipation rate than the cast iron manifold/head. I can see that it would work.

 

[addo]

I believe it works. It's also exactly why the later 2V head has a water cooled manifold (we don't do freezing here in Australia). Aluminium alloy is a good heatsink.

 

[BIGREDRASA]

Wish you guys had started up this thread before I bolted on my head without a port divider. That seems to be one probable benefit of the divider.

 

[Bort62]

Wish you guys had started up this thread before I bolted on my head without a port divider. That seems to be one probable benefit of the divider.

I'm not sure why the divider would have any affect...

 

[page62]

Wish you guys had started up this thread before I bolted on my head without a port divider.

Why can't you put the divider in now? All ya gotta do is pull the exhaust manifold...

 

[page62]

I mentioned some of the issues raised with my local guru. Here's his (slightly edited) response:

Where is the temperature sensor located? Is it in the radiator or is in on the engine in the tail end of the coolant path back to the radiator? What temperature is the sensor reading in that "tail end?"

I can assure you that if the coolant was 240 degrees anywhere in the system, you are officially boiled-over. If you get a mechanical gauge, you are trying to keep the max coolant temp in the 180-190 degree range. Most engines read the temp right at the thermostat manifold, where the temp will be the hottest.

Now here's a math problem. Which number is bigger: 240 or 600? Exhaust temp is trying to heat the intake manifold to its temperature. The coolant circulating through that plate is absorbing that heat. Even if it was 240 degrees (which it isn't), I would rather have the carb at 240 degrees than 600 degrees.

It could be a float issue, but that would show up with the engine cold as well and certainly under heavy throttle. It's worth checking, but I don't see that as the root cause of the problem.

Out in the Mojave desert it may just never been in a situation that it becomes critical. It will show up when you're sitting in traffic when the manifold goes into heat soak from no air movement to help cool it off.

So, the only suggestion that has ANY merit is the float, but only as a contributing factor, not the root cause.

 

[Bort62]

The theory that it cools the carb relative to the hot exhaust is sound, I just don't know if in practice it really makes a difference. Slade makes some valid points about temperature differntials and surface area. I also am not convinced that you have sufficient localized heating (temperature gradient) in the head to cause problems.

One would really have to do some testing to see. I should mention that I am a mechanical engineer w/ an emphasis in thermal systems, so I have some credentials here...

 

[page62]

One would really have to do some testing to see. I should mention that I am a mechanical engineer w/ an emphasis in thermal systems, so I have some credentials here...

By all means, stick some thermocouples on there and do some testing. Inquiring minds WANT to know!