MTFCA Forum

Yesterday my dad and went for about a 70 mile run with my 22 touring. This is the longest trip we have taken with it, although last weekend I put about 50 miles on it. Last weekend the car ran great and this weekend it ran great for about 30 miles. Then, while running about 35 mph, the car started surging. I would throttle down and it would clear up. We stopped to change a tire due to a flat, and when we took off again it ran great....for a while. Then it started surging again. We adjusted the carb and it didn't change anything. We stopped a few times and when we would first take off, it would run great and then start surging again after a bit of driving. When we did stop, the radiator was bubbling, but not spewing any fluids.

We pulled the carb and it was clean. Everything seemed to be in proper working order.

It almost seems like the car is vapor locking, but it never did quit all together. When I shut it off, it was not had to start again.

Any suggestions?

Sediment bowl would be my first thought.

Are you running a hot air pipe? If not try one. Dan

big2bird wrote: ↑

Mon May 12, 2025 9:55 am

Sediment bowl would be my first thought.

Me too...the "potato" under the tank is so often overlooked cause it's a PIA...

You generally don't get vapor lock while running.

I've only run one on 7 different Ts with a hot air pipe and see no difference. Have none now and they run fine.

Hot air pipes are not for winter. Ask a small piston drive pilot why they have them.
Here in south they are needed mostly in summer. When temperatures are 95+ but humidity is 100%+.
Car will idle all day fine, but get it moving and start missing. Dan

Acts like a low fuel flow issue.
Possible fuel choke points:
Partial clogged sediment bowl screen. Valve not open all the way. Partial obstruction of sed bowl inlet.
Remove the "potato" To check.
Additional fuel filter. Squeeze or necked down fuel line.
An unmodified viaton needle/seat unit.(typically presents @ highest demand)[Out of the box they are way under orifaced]
In my experience, If its a hot air pipe issue, you get a lean pop @ highest demand. Check for cold/ice build up on the intake manifold.
These symptoms lessen noticeably with a hot motor. Need for the hot air pipe largely depends on humidity & temperature.

Thank you everyone for the replies. We are in a very low humidity area so I am unsure how the hot air pipe would help. I might be misunderstanding to point of them. I will check the sediment bowl.

Shut off the gas and disconnect the fuel line from the carburetor. Put a bucket under the end of fuel line. Turn on the gas. How freely does the gas flow out? A thin stream that drops immediately from the end of the fuel line is not enough flow. The gas should stream out and arc away from the end of the fuel line. A clogged sediment screen is the most common cause, (as others have suggested).

Also, do all of the above outdoors, away from the garage!!

I don't use a hot air pipe here in Michigan - 12000 miles, no problem. If you have ice forming on your intake manifold, a hot air pipe might be helpful.
Does it surge at low RPM or only when at higher power settings? Do you have an inline fuel filter (bad idea with gravity feed)? What is your fuel line made of? Nickel-copper is a poor choice, the ends can become deformed in the carb or sediment bowl fittings - best material is repurposed steel brake line.

In addition to a plugged sediment bowl, if your tank has crud in the bottom it could be plugging the outlet. I installed a Model A type finger screen on the top of my sediment bowl in case of that problem.

Good luck!

Never hurts to check and make sure the vent hole in the gas cap is clear.

That’s very true about the gas cap being able to vent. Most any older engines need to have a fuel vent cap on it that works. I have a 54 Ford NAA tractor that was doing the surging and eventually dieing. Checked the carb, fuel bowl and etc until I had read about it in a tractor repair site. I left the cap loose and after a few hrs of use the tractor was running OK. No more chugging and dieing. Wouldn’t hurt to drill out the T cap vent hole just a little larger I think. Every T engine responds just a minor difference in different ways. After a while T owners begin to understand this. It took a while for me to figure this out.

A possible cause would be driving uphill with gas below 3 gallons in the tank. The pressure goes down with gravity flow and the carburetor needs more gas because of the open throttle. The cause could either low pressure because of the gravity flow puts the tank lower than the carburetor or the fuel line is partially clogged. This clog can happen if you have any fuel filter other than the sediment bowl or if the fuel is old and starts to gel in the fuel line. Also too small intake jet into the carburetor needle valve. I don't know whether they still sell gros jets which are a ball valve intake into the carburetor. Those were notorious for being too small to allow enough fuel to flow when going uphill.
Anyway these can cause the problem. Another problem is when there is a high point in the fuel line between the sediment bulb and the carburetor. This can cause an air bubble or vaporized gas to get in the high point causing "vapor lock". The fuel line should have the low point in the middle and slope upward toward the sediment bulb and on the other end toward the carburetor so that any bubble can go back into the tank or up into the carburetor and not in the center where it will compress and cause vapor lock.
Norm

Low fuel levels should not be a problem, until you run out, or come to a steep hill. If you need to keep filling up to keep a head of fuel for delivery to the carburetor, there is a problem in your delivery system.

Allan from down under.

I had this happen every so often and it was the coils "walking up" from their seats in the coil box and therefore causing the car to buck and surge and miss. Every once in awhile I make sure they are jammed down there and fully seated.

The lid is supposed to hold them in position ?

Many people have actually backed up hills to keep the gas flowing. I don't recommend it unless it is a private driveway. These days you would probably be rear ended if you tried it.
Norm