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Slight miss and loss of power
Posted: Sat Jan 10, 2026 5:47 pm
by 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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 5:59 pm
by 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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 6:32 pm
by speedytinc
David Payton wrote: ↑Sat Jan 10, 2026 5:47 pm
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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 6:34 pm
by 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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 8:12 pm
by David Payton
TXGOAT2 wrote: ↑Sat Jan 10, 2026 5:59 pm
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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 8:45 pm
by 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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 8:51 pm
by 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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 8:52 pm
by speedytinc
TXGOAT2 wrote: ↑Sat Jan 10, 2026 8:45 pm
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.
Re: Slight miss and loss of power
Posted: Sat Jan 10, 2026 8:54 pm
by 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?
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 9:56 am
by 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.
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 6:13 pm
by David Payton
I cleaned out the 'New Day Timer' cap and the rotating mech. and it did'nt change a thing, still missing and no power to drive down the street.
I pulled the plugs and they were needing to be regapped so I set them at .030, like I did last summer, didn't help at all.
Shorting out each plug with a screw driver while the car was running gave me no indication that anything was changing.
Changing coils around helped nothing either.
One of the guys suggested running the car in the garage once the sun is down and looking for any wires that might be arching as the car is running.
I'll do a compression test tomorrow.
Thank you all for all of the great suggestions.
One thing I forgot was when I changed the #1 coil to an extra coil I have, the car stopped sputtering but when I took it out on the street it still had barely enough power to make it home.
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 6:36 pm
by Moxie26
David.... Clean the coil unit contacts and coil box contacts with wire brush till they shine. Box contacts can be pulled out slightly to increase pressure on coils for better electrical connections. May have to use wood or cardboard strips to wedge units for tighter fit. As far as spark plug gap I use 0.025". Lastly, you may want to have someone check your coils for proper calibration.
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 8:47 pm
by David Payton
Moxie26 wrote: ↑Sun Jan 11, 2026 6:36 pm
David.... Clean the coil unit contacts and coil box contacts with wire brush till they shine. Box contacts can be pulled out slightly to increase pressure on coils for better electrical connections. May have to use wood or cardboard strips to wedge units for tighter fit. As far as spark plug gap I use 0.025". Lastly, you may want to have someone check your coils for proper calibration.
OH HHHHEEEEELLLLL YYYYEEEESSSS!!!!!
Thank you so much Maxie26. I could tell I was going to drive it further then earlier today when I backed out of the drive way and headed down my street. And into the Bakersfield 5pm traffic I went.
And I think that's as far as I've ever driven in the T using the lights.
I'm taking tomorrow off and go grocery shopping with my wife.
I think sanding down the coil box contacts with some 320 sand paper really helped. That car spent 10 years in its garage only 5 miles from the Pacific ocean and I noticed slight corrosion bubbles on the copper contacts.
Thanks so much.
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 8:57 pm
by TXGOAT2
Coil box contact issues are common. An easy way to check is to pop the lid and take out all four coils and check the contacts and springs for any evidence of corrosion or dirt. Put the coils back in and try the car out. If it runs better, clean the springs and coil contact buttons and put the coils back in with cardboard shims on the driver side of the coil box. Shims cut from cardboard from something like a macaroni box usually work well. Fold them once and slip them between the coil unit and the inside of the box. Your coil box lid should have a gasket to keep water and dust out. New ones are available if yours is deteriorated or missing. The lid should snap down firmly, since it serves to hold the coils snugly in the box.
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 8:59 pm
by TXGOAT2
The car should start easily and run smoothly without missing, bucking, jerking, or backfiring. It should not shake or shudder when shifting from low to high.
Re: Slight miss and loss of power
Posted: Sun Jan 11, 2026 9:04 pm
by Moxie26
David .... Check your grocery list against the coupons you have.,.. makes a trip more exciting and your wife will smile.
Re: Slight miss and loss of power
Posted: Tue Jan 13, 2026 3:26 pm
by David Payton
So doing a compression test I have now discovered that my main problem is actually a stuck open exhaust valve on cylinder #3. I've cranked the intake valve down and closed and put some ATF and penetrating oil in. I'll leave that in #3 and see what happens.
Re: Slight miss and loss of power
Posted: Tue Jan 13, 2026 4:01 pm
by Bill Robinson
David, if you have any, or have access to some Marvel Mystery Oil, try putting about a tablespoon full in each cylinder through the spark plug holes, hand crank the motor a turn or two, and go off and leave it. Then tomorrow go out and start it. It'll smoke alot, but when the smoke clears it should run better. I learned this old timer's Model T trick from the MTFCA Forum years ago, and it clears up stuck valves, stuck rings, etc. But, the motor will have to sit for a while before things get loosened up.
Re: Slight miss and loss of power
Posted: Tue Jan 13, 2026 4:19 pm
by South Park Zephyr
I fought this issue a couple of years ago. After checking / rechecking everything, a fellow club member suggested changing the coils. Since they were recently rebuilt by a well know coil supplier, I though that cannot be the problem.
Well, as you can guess that was the problem. A capacitor failed. The man who did the coils stood behind them and fixed the problem for me.
So, if in doubt, recheck everything.
Scott
Re: Slight miss and loss of power
Posted: Tue Jan 13, 2026 5:05 pm
by TXGOAT2
The hardest issue to find is the one you know is OK, but isn't.
Re: Slight miss and loss of power
Posted: Tue Jan 13, 2026 5:55 pm
by Moxie26
Bill Robinson... I thought of posting the same thing about Marvel Mystery Oil. .....I did that 15 years ago to friend's 25 coupe and the valves freed up and the car ran great afterwards..... after the smoke from the exhaust cleared out !
Re: Slight miss and loss of power
Posted: Wed Jan 14, 2026 8:31 am
by Bill Robinson
Robert Jablonski- back not long-after regular gas changed to "Ethanol Gas" Suzi and I went on a Tennessee T's club tour. My 25 Touring Car was running good. Then, after unloading the car, I went for a test run. It ran great, until....... it started missing real bad and we barely made it back to the motel. Lynn Cook, one of our older members at the time, suggested that I pour Marvel Mystery Oil into each cylinder and let it sit. Well, his advice worked! And, over the years since, MMO I have it used several times and I'll use it again. Lynn, if you can hear me up there- THANKS FOR YOUR HELP!
Any parts store will have it.
Re: Slight miss and loss of power
Posted: Wed Jan 14, 2026 9:23 am
by love2T's
David Payton wrote: ↑Sun Jan 11, 2026 8:47 pm
Moxie26 wrote: ↑Sun Jan 11, 2026 6:36 pm
David.... Clean the coil unit contacts and coil box contacts with wire brush till they shine. Box contacts can be pulled out slightly to increase pressure on coils for better electrical connections. May have to use wood or cardboard strips to wedge units for tighter fit. As far as spark plug gap I use 0.025". Lastly, you may want to have someone check your coils for proper calibration.
OH HHHHEEEEELLLLL YYYYEEEESSSS!!!!!
Thank you so much Maxie26. I could tell I was going to drive it further then earlier today when I backed out of the drive way and headed down my street. And into the Bakersfield 5pm traffic I went.
And I think that's as far as I've ever driven in the T using the lights.
I'm taking tomorrow off and go grocery shopping with my wife.
I think sanding down the coil box contacts with some 320 sand paper really helped. That car spent 10 years in its garage only 5 miles from the Pacific ocean and I noticed slight corrosion bubbles on the copper contacts.
Thanks so much.
All excellent advice from Moxie. Ya need to clean contacts usually about every 2 years. At least I do and it helps. One other thing I didn't see but didn't read this very long thread ha ha...was to "try" to check for carbon tracking. It's usually pretty invisible is the problem. However, if the wood in your coil box isn't in good shape I'd definitely rebuild the box with the newfangled "plastic wood" the vendors sell. I did that on one suspect car and it did the trick. Just sayin.