'24 hot air tube to carb

[Guest occrj]

Hi all,

Mine doesn't have an air tube fitted to the inlet of the carb, does anyone have photos or a diagram showing what it should look like?

I noticed that after running the engine for some time, up and down the road a couple of times etc, there was condensation on the outside of the carb. Is this likely to be because I'm missing the hot air tube?

Thanks for your help everyone

RJ

[Pete K.]

It is only a small sleeve about 1-3/4" long that is rotated by hand for more or less opening in air tube. It has a slot and a dimple that rides tightly in a small slot in air tube. You could make one up pretty easily in a pinch. I don't see these for sale by themselves, usually, it is still on an old carb. I don't think I have a shot of one in my photo file but I can get some if someone doesn't do that sooner. Last fall, when I had my '25 started up, I, too, noticed frost on the iron part of the carb. The air tube was only cracked open a bit and frost went away when engine warmed. That part of the carb is just outside of the big venturi of the Dodge carb and I suspect this was a common occurrence back in the day. It has to do with some Law of Nature, air speed increases, (in the venturi), temperature drops, or something like that. Frost will form. I believe this is why aircraft air foils ice up without de-icing devices in place.----Pete.

[Pete K.]

RJ, Got thinking about your question some more and I wonder if you're talking about the "other" hot air tube, located on right side engine, connecting exhaust manifold with the passage between the block. Let me know.

[MikeC5]

Mine is missing that one...

[Guest occrj]

Hi Pete, I have the small rotating piece on the inlet to the carb, but there's nothing that passes through to the manifold side on my engine. Rgds, RJ.

[Pete K.]

My '25 has the horn shaped oval tube from the bottom center of the manifold then passes through the valve covers, about an inch, at the center of the block. There it stops. the entire bottom edge of the sheet metal tube has a spot welded rib seam with a notch in it to help stabilize the tube once it's in place with the valve covers holding it. It is extremely difficult to get everything back in place when having to have the valve covers off. I can see why many are missing. At one point, I wanted to chuck the blasted thing across my yard. I believe the tube itself was painted black gloss enamel, or lacquer. Without this tube, I don't see how the carb could ever get enough hot air on start up, or rather warm up.

[Guest occrj]

Interesting, thanks Pete, so the pipe doesn't run all the way to the carb, it just pokes into the opening in the centre of the block? Have I got that right? thanks, RJ

[Pete K.]

Yes, Pokes through the valve cover's only a short bit. I think they made the tube slightly oval so that it doesn't rotate and fall off it's mounting flange on exhaust manifold. There is no clamp on this tube. The lower notch in the tube rests on the two valve cover's openings. It seems a very likely "rattle trap" when car is in operation.

[Guest occrj]

Hmmm interesting stuff, it'd be interesting to see a photo of its installation if possible sometime? The weather's not particularly warm here right now, and iirc the shutter was fully open when I looked at it, so the combination of shutter open and no pipe from the manifold could cause running problems after a while...I must admit it's the first time I've seen the outside of the carb wet all over with condensation with the engine running.

[Pete K.]

Here's a picture of the heat tube installed on the engine. The notch is at the top of the seamed tube, not the bottom. Tube fits into the cast iron opening of the manifold and is held by the two valve covers. Believe me, it's not an easy task to install it when replacing the valve covers. There is just no room to finagle the valve covers over their wing nut studs and overlap the rear cover onto the front cover while trying to get the heat tube to stay put with the notched seam in the right place.

[Guest occrj]

Thanks for posting that Pete. I'll have a look at making up something as a stop-gap measure next time I pull off either the manifold, or the mag, for better access. I notice that my manifold has a tiny screw in it close to where the tube fits to the manifold, on the lowest edge, presumably to locate the tube a little. I'm hoping that just by closing the shutter on the carb (it was wide open), it'll draw in warm air from within the "tunnel" rather than ambient, and help engine running even if it's not the entire solution.

[MikeC5]

Yes, thanks for posting it Pete. If you do have to remove it again for some reason I would be interested to see the entire thing from a few different angles.

[Pete K.]

I wish to heck I took a photo of that heat tube the day I had the valve covers off. I don't seem to have any set screw on manifold to help keep tube steady while installing it. There's not much more to it, other than the "angle" of the tube & the diameter of each end which could be seen on the manifold and the valve cover openings of the Dodge.

[R.White]

Here are a some shots of my 'hot air to carb'. The pipe is slightly different from the earlier one in that the casting extends through the hole formed by the valve covers. The hole is oval because the pipe fits at an angle. I think this is easier to assemble than the earlier design. Despite being slightly damaged, it works and the car starts easily.

[JayG]

There is a collar that is bolted inside of the valve chamber. That and the valve covers keep it aligned and rattle free. You can see it in the center of the valve chamber. Unfortunately I didn't take any pics of the tube.

[R.White]

I guess the collar would also have been fitted to my engine but it is missing.

Ray.

[MikeC5]

Interesting... I assumed it would have extended to the carb. Occrj, I have also noticed the condensation form on the upper chamber of the carb and it did feel cool to the touch. It may be an evaporative effect from the fuel/air mixture passing through.

[Pete K.]

It's called Bernoulli's Principle. Air speed increases, (in a venturi here), the pressure drops with the temperature also. The carb will feel cold and you may see frost on carb with the ambient air just right. Ray, your '26 hot air feed is quite different than the earlier set up. Your '26 also has the air filter. Although the miles I've put on old cars without air filters, I've not seen any difference in engine wear or polluted oil in a faster rate, probably since the cars are driven infrequently enough and most all roads are paved. I've looked around my barn and yard yet cannot find even a rusty spare heat tube for a '25 or earlier Dodge. I'm sort of surprised since many early Dodge parts are around here. I did find the remnants of an early Dodge Brothers manifold heater and control linkage.