Slight miss and loss of power

[David Payton]

Last week my 26 sedan ran so great but this week there’s a slight missing in the exhaust and a noticeable loss of power. And when I shut the engine off there’s a noticeable vapor coming out of the choke. 🫤 shorting out each spark plug seems to have no noticeable change in engine sound.

[TXGOAT2]

If you see some vapor at the carburetor air inlet after shutting the engine off, it's probably normal. If it puffs vapor out the carburetor when the engine is running, it may indicate an intake valve issue, such as a weak spring or sticking valve. Do you have an original type timer? If so, it may need oiling, or cleaning and oiling. If your car has been exposed to rain or high humidity, dirt on the spark plugs or moisture on or in the coil box may cause a miss. If the car isn't driven very far at a time, or very often, just driving it on the open road for half an hour at 30 to 35 MPH may clear up the problem. Be sure you have fresh gasoline in the tank. Modern gasoline decays, and it can cause a number of problems in cars that are not driven often. Model Ts don't like thick oil. If your oil is dirty or thick, change it. 10W30 oil gives good service under all but extreme conditions.

[speedytinc]

Last week my 26 sedan ran so great but this week there’s a slight missing in the exhaust and a noticeable loss of power. And when I shut the engine off there’s a noticeable vapor coming out of the choke. 🫤 shorting out each spark plug seems to have no noticeable change in engine sound.

Shorting each plug, the engine should run rougher when you short the cylinder @ fault. When doing this look for a healthy spark jump from your screwdriver. If you find that cylinder that makes no difference in engine smoothness/roughness, thats the one. Switch coils on that cylinder & see if the fault moves to the coil you changed. Check the timer. Pull the plugs looking @ the electrodes for evidence of not firing, leaner, richer or wetness.

[John kuehn]

Try to park your car in a dark garage or raise the hood and start and run the engine at night. Watch for any sparking or intermittent sparks around the wiring and coil box. Sometimes a loose or shorting wire can cause a miss. Just a guess of course. I found a short causing a miss on my 24 Coupe that way.

[David Payton]

If you see some vapor at the carburetor air inlet after shutting the engine off, it's probably normal. If it puffs vapor out the carburetor when the engine is running, it may indicate an intake valve issue, such as a weak spring or sticking valve. Do you have an original type timer? If so, it may need oiling, or cleaning and oiling. If your car has been exposed to rain or high humidity, dirt on the spark plugs or moisture on or in the coil box may cause a miss. If the car isn't driven very far at a time, or very often, just driving it on the open road for half an hour at 30 to 35 MPH may clear up the problem. Be sure you have fresh gasoline in the tank. Modern gasoline decays, and it can cause a number of problems in cars that are not driven often. Model Ts don't like thick oil. If your oil is dirty or thick, change it. 10W30 oil gives good service under all but extreme conditions.

Thanks TXGOAT2 it's not puffing out of the carb. It has a 'New Day' timer on it, I'll pull it off and clean and oil it, I was told by the local T guys to put only a bit of light oil in it. The car has always been garaged. I just put 8 gallons in it last week. When I bought it last July I changed the oil and lubed and greased everything I could find to lube and grease. This car has Ruxtel, Rocky Mountain brakes and Multi-lift Jr. valve system.

[TXGOAT2]

The New Day timer may need cleaned or refurbished, but it does NOT need oil! I have no experience with the Multi-lifts, but you may have a problem or adjustment issue with one of the units that is affecting valve seating. Other possibilities are a worn timer brush, rough surfaces inside the timer, a coil adjustment issue or a coil point set issue. I can only guess from here. It's often possible to inspect the spark plugs to get an idea of which cylinder may be missing. If one plug looks much different from the others, it may indicate an issue with the plug or coil or valves in that particular cylinder. You can also run the engine about 5 minutes, then shut it off and set the parking brake and leave the ignition off, then use the hand crank to pull each cylinder through its compression stroke. Pay attention to any difference in the effort required to pull each cylinder through, and listen for any hissing sounds at the carburetor or exhaust or oil filler that might indicate compression loss.

[speedytinc]

Well thats a new kettle of fish.

New day timers must run DRY. No oil. Cam needs to be sealed from any oil getting to the timer.

Check that all the multi-lift arms are working full function. Check for valve clearance. They had the habit of shearing the pivot pins.
I tried a set of nos units once. The lift arms ate away the valve stems & several pins were loose & sheared. #4 exhaust valve wasnt opening enough, hence rough running & a lack of power. Thats why I opened the valve chamber up & found the carnage.
Very disappointing experiment.
Yours look good @ the moment. Maybe a compression test will show a valve or 2 not closing all the way.

[speedytinc]

The New Day timer may need cleaned or refurbished, but it does NOT need oil! I have no experience with the Multi-lifts, but you may have a problem or adjustment issue with one of the units that is affecting valve seating. Other possibilities are a worn timer brush, rough surfaces inside the timer, a coil adjustment issue or a coil point set issue. I can only guess from here. It's often possible to inspect the spark plugs to get an idea of which cylinder may be missing. If one plug looks much different from the others, it may indicate an issue with the plug or coil or valves in that particular cylinder. You can also run the engine about 5 minutes, then shut it off and set the parking brake and leave the ignition off, then use the hand crank to pull each cylinder through its compression stroke. Pay attention to any difference in the effort required to pull each cylinder through, and listen for any hissing sounds at the carburetor or exhaust or oil filler that might indicate compression loss.

Cant argue with any of this.

[TXGOAT2]

The Multi Lifts might work better with a set of stainless steel valves. That's a LOT of lift... do they use stock Ford springs?

[TXGOAT2]

A valve issue related to valve springs or keepers or the Multi Lifts may not show up on a compression test, whether using the crank and "feel", or using a gauge. In some situations, a valve may seat at very low speeds, but fail to fully seat at normal operating speeds.