**CARB ICE**

[Professor Fate]

Drove the '26 today and it ran poorly. Investigation revealed a wet exterior of the intake manifold.
I think I was making ice internally with the temp and dewpoint so close today. Very damp and raw.
Car would run great ceuising at just less than half throttle and mixture adjusted. Any advance or movement of the throttle caused it to gag, sputter, and pop ever so slightly. NH carb, stock intake, stove pipe.
Thoughts???

[TXGOAT2]

The heat pipe is supposed to take care of such issues. If it is in place and working properly, I don't know much else you could do except try running the timing a little late to get more exhaust manifold heat. If you have a water pump, removing it might help. A different gasoline blend might be helpful. Under severe conditions, running the engine a little harder with timing set a little late ought to get a lot of exhaust heat. Stopping the engine for about 3 minutes will often clear up cold intake problems. Then restart and run with late timing and try to keep some load on the engine. If the engine is misfiring, the exhaust may be cooler than normal. You should have enough manifold heat if the engine is running on all 4 to keep the intake warm enough under most any condition.

[Professor Fate]

I don't run a water pump or a thermostat. The combo of the new Brassworks radiator and the '26-'27 improved car fan which is mounted higher, seems to be hyper cooling the motor.
In Summer, I barely see 180f on a 90f day.
After a good 10 mile ride home, the top of the radiator was about 140f.
Before I left the house, I had thought about hanging a piece of cardboard over the bottom half of the radiator. I might try that.
I've had carb ice in airplanes many times. Classic symptoms of it in the T confirmed by generous condensation on the intake manifold.
The stove pipe was very warm to the touch. But the intake manifold was quite cool and wet.
As I ran the car the motor would run smoother briefly, but never shook off the icing condition.
It would actually regress back to rough running/building more ice, with throttle position changes and mixture adjustments.
It just didn't like a damp and raw 50f New England Fall day...

[TXGOAT2]

I'd try cardboard over the radiator to get more underhood heat, and be sure the heat pipe is positioned correctly. Removing the fan belt might help. Late timing will get more heat to the intake and allow more throttle opening at a given speed, which should help with an icing condition. Don't run for extended periods with very late timing. About 1/4 to 1/3 less advance than normal should be sufficient. Be sure some other issue, such as fuel filter restriction or plugged fuel cap vent is not in play. Also be sure ignition is clean and dry. Damp, cool weather will aggravate otherwise insignificant ignition issues such as dirt on plug insulators or any wiring or coil box problems. Some condensation on the exterior of the intake is normal, but it does suggest a cold intake issue. Getting more underhood heat would tend to work against both cold intake problems and any damp ignition issues.

[RajoRacer]

"Cool & wet" is quite different than "Icing" - if the manifold had actual ice, then you need to address that issue with pre-heat.

[Professor Fate]

"Cool & wet" is quite different than "Icing" - if the manifold had actual ice, then you need to address that issue with pre-heat.

The internal icing condition was making the outside sweat. If the outside was ice, then the car probably would not be running at all.

I'm gonna wipe the timer out too just in case.

[RajoRacer]

I had an"icing" issue with my overhead here in the P.N.W. moist air conditions - remedy was a heat stove off my header directly into the carburetor throat. I'm not familiar with the term "inside icing" but have seen condensation on intake manifolds. It appears I won't be of assistance with your problem.

[aDave]

I believe the OP is stating that ice is forming inside his intake manifold...causing the manifold to become quite cold, resulting in the humid outside air coming into contact with the manifold, becoming colder and losing its moisture...thus the condensation. Your previous statement of "pre -heat" is right on.

[Professor Fate]

"Inside icing" refers to the internal passageway of the intake manifold actually building ice, restricting air/fuel mixture flow to the engine. As this ice builds, and you change power setting enough to allow the heat from the stove pipe to melt the ice, performance will suffer further as the engine ingests melted ice (water). Performance is only restored when the ice has melted and the water produced by melting has been sucked thru the engine.
In an airplane one can pull "Carb heat" to melt the ice. On a model T the carb heat is on all the time if equipped with a stovepipe.
The conditions I experienced were the perfect storm of icing, not allowing the stovepipe heat to prevent ice.

[J1MGOLDEN]

You have to understand the Venturi Effect to understand the icing problem.

[Professor Fate]

That chart is awesome!

[Professor Fate]

"Hot Spot?"

C4B27E01-A19E-4515-A2FF-B32BBE6F2F75.jpeg (51.94 KiB) Viewed 1738 times

3

[TXGOAT2]

A T engine would benefit from a well-regulated hot spot arrangement. Under severe conditions, both intake air preheat and a hot spot would be beneficial. Some newer vehicles have rather elaborate manifold heat and intake air preheat systems. They work very well when they are in good condition. If you live where icing/condensation are a frequent issue, modifying the heat pipe to collect more heat may be an option. The exhaust pipe from the manifold back to about the hogshead gets very hot very quickly, and putting a sleeve around it that is attached to the stock heat pipe would probably be helpful. A damper arrangement to prevent excess heat would likely be needed.

[RajoRacer]

I agree Pat - I need to make mine adjustable for warmer weather !

[Professor Fate]

What about using one of those production bolt on heavy cabin heat shrouds and ducting the air to the carb.? I'd want some kind of controllable flap to increase and decrease hot air intake.

Just thinking....