MTFCA Forum

I’m presently bringing back a 1924 Model T pickup that my grandfather put together from parts around 1980. Presently I’m perplexed by two things. After running and everything being up to temp, I have condensation around the connection between the carb and the intake manifold. I recently rebuilt the carb and replaced the intake/exhaust manifold gaskets and painted both manifolds with high temp paint. Is this normal or does this point to some issue? Also, I can’t seem to understand why whether warmed up or cold, sometimes it’s very hard to restart. Even jacking up one tire and putting it in high gear won’t help. Otherwise it runs like a top. Starts on compression at times as well. Any advice is welcome. Thanks

Mike

Typical when running without the factory hot air pipe. I only run my hot air pipe in the winter, the rest of the year I run a home-made air filter.

That is why FORD supplied a hot air pipe on the car. High humidity even with warm weather, and many of these cars will do this. When they do, the fuel will not remain atomized to the proper extent and you often have to run richer as though the vehicle is actually running in very cold weather. When I lived in FL, this was a problem particularly with my '13 and an aluminum intake...I had to run rich enough to keep running, but would tend to foul #1 plug. Adding a hot air pipe solved the problem and I found I could run the carb another 1/2 turn leaner...plugs remained clean, car ran fine, and restarting was not a problem. If you're interested in the technical reason, look up Bernoulli's Principle. It will explain that as the flow of air accelerates through the throat of the venturi, pressure decreases and among other things, because volatile fuel is involved, it drops the temperature, enough to condense moisture. That's what you're seeing, but it is the chill of the intake which plays havoc with the vaporization of the fuel...and that's what you're experiencing.

That said, prepare to be told that you are not seeing what you're seeing...there are plenty of guys in dry climates who have never seen this phenomenon and will be all to happy to tell you that you're doing something wrong. You're not. Just find yourself a hot air pipe and this problem will be in the rear-view mirror very quickly.

Good advice as usual Scott. I've had engines almost boiling over while at the very same time the lower section of the intake was ice cold and forming water drops. The hot air tube fixes it. I also believe that the lack of a hot air tube contributes to the "runny nose problem" that Stan referred to with some Stromberg OF's.

Mike,
I agree 100% with your prior answers. But I do like to provide direct answers to questions:

You asked in your original post: "Is this normal or does this point to some issue?"

My direct answer is: "Yes, the condensation on your intake manifold connection is absolutely normal and to be expected."

The three prior posts told you how to fix this common phenomenon. They're all 100% correct.

To help you understand why the condensation occurs, think of it like this: The air coming into the carburetor is warm and moist. When it is mixed with gasoline, the gasoline evaporates into the air. That evaporation cools the fuel/air mix quite significantly. Leaving the carburetor and entering the intake manifold, the air is extremely cold -- as much as 40° colder than when it entered the carb. That cold fuel/air mix is so cold that it chills the intake manifold and condensation forms on the cold manifold. The condensation also occurs on the inside of the manifold, sometimes causing a build up of frost which can cause the engine to stumble or even quit.

The solution to this problem is to pre-heat the incoming air so that, in spite of the 40° temperature drop, the mixture remains warm enough not cause condensation or frost. Thus the "Hot Air Pipe".

Really enjoyed reading this post. Great practical and informative answers to a common occurrence . Well done to all.

Scott, How does fitting a hot air pipe shift the condensation to the rear view mirror, and is it only to the centre mirror?

Allan from down under.

The condensation is normal under some conditions. In cooler weather, frost can form. It is due to the same refrigeration effect that air conditioning works on. A gas expanding into a region of lower pressure will become cooler. Cooling is also due to rapid evaporation of gasoline. The combination of these effects can chill the manifold far below freezing. Hard starting may be due to an ignition or carburetion issue, or it may simply be that you haven't yet figured out the best procedure for starting this particular T under various conditions. Any issues related to the cold manifold will usually disappear once the engine fully warms up in mild weather, or when the engine is stopped for a few minutes, then restarted. Stopping the engine stops the refrigeration effect, and ambient heat soon warms the carburetor and manifold, except in very cold weather. In cool, damp weather, starting the car and driving away will often prevent condenstation and freeze-up, since the engine will warm up rapidly when moving the car, and the more the throttle is open, the less the refrigeration effect. The refrigeration effect is most pronounced when the engine is cold and the throttle is at idle or near it. Opening the throttle and loading the engine reduces the pressure drop at the throttle plate and raises the manifold pressure, which works against the refrigeration effect. This problem occurs under some conditions in all throttle governed gasoline engines which lack some method of heating the manifold and throttle area of the carburetor.

The selective mirror fogging is caused by the same gremlin that causes large bugs to impact the windshield directly in the driver's line of vision. Do not anger the gremlin, or it will direct large pebbles to impact the windshield directly in the driver's line of vision.

I have never, ever experienced this phenomenon until I installed my "new" Holley G. After running a few minutes at low idle I did notice condensation on the lower end of the intake manifold. So far, "it don't hurt the runnin' of it none". As I drive on country roads a lot, I run an air filter instead of a hot air pipe. I won't change that unless the intake ices up and becomes a problem.

There are several versions of he hot air pipe - I am in the process of adding them to the classifieds

Probability of icing chart

Yes. Install a hot air pipe for the icing. Now on the hard to start issue.I agree with txgoat about finding the proper procedure for starting your car. I believe each T has its own personality and you have to find yours by trial and error. My 1915 requires one stroke with full choke and key off when hot. One other thing that I've noticed over the years is that my car HATES an audience. If there is more than three people watching you hand crank, it won't start no mater what you do. As soon as they walk away and the sweat dries, she will start right up. bobt

I'd stick with the excellent air filter you have installed. If you have significant issues with cool weather operation, you could get a late style repro hot air pipe and cut it off and make an adapter, maybe from a tin funnel and a coffee can, to allow at least some hot air off the exhaust manifold to reach the intake.

If there is more than three people watching you hand crank, it won't start no mater what you do.

Mister Ed talked to Wilbur when nobody else was around.
If anyone else was there he wouldn't say a word.
I call my T Mister Ed.

WILBUURRRRRRR!

Back when I was learning to fly, we were taught that carburetor ice can form at any temperature below 70 degrees Fahrenheit. Strangely, at extremely low temperatures, ice is rarely an issue as the air doesn't contain enough moisture for ice to form.

Condensation/icing will occur in cool, damp weather if humidity is present. Dry air cannot deposit condensation, thus wetness or frost cannot occur. I have an old Ford truck that starts easily in any weather. In cool, damp weather, it will not idle or run slowly for any length of time without the idle jets icing up. After a few miles, the problem disappears as the engine warms up and the underhood environment gets warm. In dry weather, there is no problem. The reason this happens in this case is that the manifold heat valve and intake air heat devices are non-functional. Neither is the automatic choke, but that doesn't contribute to the condensation/icing. Condensation inside the carburetor and inake manifold can cause poor idle and excessive coughing/backfire until the engine warms up. Frost in the carburetor and intake can make running the engine difficult. Symptoms are similar to a cold engine needing a richer mixture or partial choking, but the cause is not the same and using the choke or richening the mixture may not eliminate the problem. Once the engine compartment warms up as hot water begins circulating, the problem will vanish under normal conditions. It may persist under extreme conditions unless some type of intake air heat is provided.

Condensation will occur at pretty much any temperature if there is sufficient humidity.

Florida in August: 96F - 85% RH...been there, done that

The presence of condensation is not a cause for poor atomization; it is however a visual signal of the chilling going on and the poor atomization that you can subsequently expect.

A nifty Dew Point calculator is here: http://www.dpcalc.org/
You can see quickly and clearly how easy it is to get an intake to "sweat" even in warm/hot weather if the humidity is high enough.

Some people chose to fight it, and others relent to the laws of physics and thermodynamics and fix it.

Cold drinks will warm up much faster in warm, humid weather than in dry weather at the same temperature. Ice will melt more rapidly, too. A cold soda will "sweat" copiously around here in 98 F weather with high humidity. An auto air conditioner may become unable to adequately cool a vehicle on a day with high humidity and 95 F temperatures. The same air conditioner can overcool the same vehicle on a 105 F day if the humidity is low. Endothermy/exothermy. Liquid to gas, gas to liquid. New Orleans at 98 F is very different from Salt Lake City at 98 F.

I believe that high humidity can reduce evaporation rates of volatile liquids if all other factors are the same. The main problems with moisture or frost accumulating in carburetors is physical obstruction of idle jets and the gap around the throttle plate at idle and low speeds. Cold air and a cold intake tract will restrain gasoline vaporization even in the absence of of humidity.

I noticed Arizona never occurs on that chart. One of the best performance mods I have done was take the hot air pipe off my other T. Made the comparison on a tour that was mostly model A's & speedsters. I had the most stock & heaviest car on the tour and struggled to keep up. When I took off the pipe I was almost able to keep up. I have no idea why I put it on in the first place? Back in the 1970's we took the heat riser tube off new cars so they would run better. That was part of the emissions mods the MFG's came up with. I'm sure it worked in most of the country, but didn't do anything for a car running in 100+ degree temps. with 10% humidity.
Craig.

Wow, I had no idea this forum would be so active! Thanks to all for the responses and info.

I was concerned that the condensation meant I may be running too lean and not allowing enough gas to maintain warmer temps.

You all have convinced me that I need a warm air intake. I’m liking the idea of the condensation causing the restarting issue as it happens sometimes and sometimes it does not and it was starting to drive me nuts as this T runs extremely well and strong…when it runs.

Another question: did Henry design the engine with an air filter or is that one of the myriad additions?

I really appreciate the help as I have a ton of questions. I’ve grown up in old Fords as my grandfather was a collector. I’ve gone more miles than most in a ‘12 Model T, Touring. My grandfather was a natural mechanic/engineer and I’ve seen him cure many an ailing T in the shade of a tree. Sadly we lost him last December just before his 96th. It’s now my goal to keep this old girl running and pass along the love of them to my girls. I appreciate the support in my endeavor.

I’m hoping to find more in our hobby in NW IN. Seems so many center around central Indiana. If anyone is from the Anderson/Muncie area and have been in the club a while we likely know each other. I’m Mike McCully and my grandfather is Bill McCully.

Thanks again for the help.

Mike

Never came with an air filter. Some successfully run them, though I could never make any of my 4 "T"s work properly with one.

I never understood the willingness to pay top $$ for a straight-through NH for the very modest increase in air flow, and then in the same discussion listen to folks who don't worry about the lost CFM due to a filter. My advice to folks who worry about their "T" ingesting dust is this: "Drive up front"

welcome to the hobby

As others have stated, " carburettor icing is real."
And as others have stated, in some parts of this country it never occurs.

More photographic proof of icing on the manifold and carburettor when the hot air pipe is absent. The engine was running poorly (like crap) and the hot air pipe "fixed" it.

Around here, dust is unavoidable in dry weather. I use a foam sock type filter, lightly oiled. It keeps the airhorn of the carburetor sparkling clean. It doesn't seem to affect the performance much. The car is routinely driven at over 40 MPH and fuel economy is good to excellent. I'd like to add a Donaldson-type dry air filter such as many small tractors have. Lack of a hot air pipe has not been a serious problem here. Ideally, a carburetor with a filter would have the bowl vented to the airhorn ahead of the choke plate. If the filter is a low restriction type, it will work fine vented to the atmosphere as long as it is of sufficient size for the CFM and is kept clean. The altitude here is around 1100 ft. Operating at higher altitudes would make having a low restriction air filter of paramount importance.

For those chosing to run an air filter, be absolutely sure it can not collect fuel (from over-choking). In my 61 years of playing with Model A's and T's , I've known 3 to have been totally destroyed by fire originating in the add-on air filter. One was a '29 A that I had just restored and the new owner insisted (against my advice) that it needed an air cleaner. He was able to save one stainless tail light.

On my first trip to Spokane I bought a cast aluminium adaptor made by one of the Inland Empire T owners. It is an elbow which is held in place on the intake lip of the carburetor with a grub screw. A K&N filter hangs vertically and below the carburetor. The combination is easily serviceable and has no effect on performance. I'd like to make a few more some time.

Allan from down under.