MTFCA Forum

I finally got my 1914 Model T touring running and have been testing on short trips. It starts and runs well, but when it gets hot it stops running and will not start until it has cooled off. It has spark, but does not seem to be getting any fuel after it quits. Even though it is a 1914 car it has a Holley NH carburetor that has been rebuilt. The radiator is almost new and the cooling system seems to work quite well. The spark is good and the problem happens on both battery and magneto. The fuel is fresh and there is a new filter and a second brass filter on side of the carburetor. When it is cold I choke it until the carburetor drips a little fuel and then turn on the switch and it starts in a couple of pulls.
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Here is what I know....When the car is hot and it quits I can choke it and crank away and no fuel runs out of the carburetor. When it cools off I choke the car and things are back to normal and it starts.
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Here is what I tried. I thought it might have been a stuck float valve so I tried tapping on the carburetor and it did not help. I tried replacing the float valve with another one and it did not change anything.
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I thought it might be a vapor lock problem so I wrapped the exhaust and the fuel lines to shield the fuel from heat. I also made sure the fuel line had a low spot in the middle so any bubbles would go back to the tank or towards the carburetor and not be trapped in the middle. This did not seem to change anything either.
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I tried all of these things and the car will still start cold and run fine for 15 minutes or so and then have a fuel problem. Any ideas of what to try next?

Check the vent hole in the gas tank cap.

Remove the fuel filter/filters and run it without. Fuel filters cause exactly the symptoms you described.

YES.Remove the filters. My T's don't like filters and the sediment system works well if your fuel tank is clean and not rusty.

All three ideas fit the symptoms described. All restrict the fuel flow. Next time it stops, turn on the tap in the fuel bowl and see what comes out.

Allan from down under.

I’ve just been through the exact same issue with a 1914 T
Fuel line increased to 5/16”, vented fuel cap, NH Carby but no fuel when hot (20 minutes drive)
Condenser and Coil changed ( Distibutor Ignition )
Engine operating temperature normal
Fuel tank opened up and cleaned out
No sediment bowel on the tank.
Carby swapped to a known one, to eliminate sticking needle / seat.
Inline fuel filter removed and relocated in the bin
Engine compression good.
We narrowed it down to fuel! Fuel tank over half full.

We set up a seperate fuel tank positioned in the front seat with a direct hose to the carby. Problem gone!!
Re routed fuel line well away from the exhaust in the most direct path to the engine minus the filter
All good, happy days
Alan in Western Australia

On most of the cars the fuel tank is under the seat. Some even have it under the back seat. On the cars with the tank under the seat, they get the most fuel to the carburetor when the tank is over half full. Lower fuel will actually cause the car to stall when going uphill.
another problem is the routing of the fuel line. It should go from the seat to the lower side rail of the frame. crossing the exhaust pipe, but the part running parallel to the exhaust several inches away from the pipe. There should be only one low point in the line with the line going uphill toward each end, at the tank and at the carburetor. that way any air or vapor bubbles will rise to either the tank or the carburetor. They also run best with only the sediment bulb under the tank and no other filters. The screen on the sediment bulb should be intact and clean. Also note, if the car has been stored a long time, the fuel in the line can get like varnish and block the flow. In that case, it might be necessary to replace the fuel line.
Norm

More information needs to be given as to the cause of the OPs specific problems, however with regard to statements made that cars often need 1/2 tank or more to get up a hill, there is a simple explanation: Because all of the commercial float valves available at the major suppliers (and they all carry the same thing) are made with a through-hole that is only about 50% of the flow area of the correct valve. You can play games with 5/16" fuel lines or even fuel pumps if you are inclined, but that is treating the symptom and not the Root Cause. You still are trying to squeeze the fuel past a restriction limitation that the design of the car was not built to operate properly under.

To treat the root cause of the problem, you can view a solution to that problem in the classifieds, here: viewtopic.php?f=5&t=18321&p=171886&hili ... ow#p171886

commercial valve on the left, solution on the right

Thank you everyone for your advice. I am going to take out both fuel filters and replace the fuel line so everything will be new between the gas tank and the carburetor. I also plan to wrap the entire fuel line with a heat shield to reduce the chances of a vapor lock in the future. I also like the idea of having a higher flow valve in the carburetor and I plan to look into getting one of them also.
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I will post my findings after I make the changes.
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Thank you again.....Bryan
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Also, check the sediment bulb and its internal screen. If you open the draincock on the sediment bulb, does gas come out? If not, means that you have dirt collected in the bulb such that gas can't pass. Also, may mean that the dirt is piled up as far as the fuel outlet and also blocking the screen.

I really don't think your car being hot has much to do with your problem. It's simply that you don't have enough fuel flow and the engine runs until the carb bowl goes dry. Waiting a while allows it to refill, run another 15 min. & die.

Bryan-
It's unknown how long you have had the car so I am going to presume it is fairly new to you car. The filters may have been due to a poor quality fuel tank and crud in it. As the car rattles stuff gets stirred up and blocks the line. Shutting down allows it to filter thru. The easiest way to determine if this is the cause is run an external tank to the carb, a boat fuel tank works well with some rubber line.

It would be beneficial to know if "shuts off when warm about 15 min if that is under load or idling. Just as what your definition of "cools down" is. When it has shut down and is "hot" it would be a good idea to pull the bottom off the carb and see how much fuel is flowing thru the valve. If it really is something dealing with the "heat" of the engine it may be possible for the manifold to develop a leak where it won't pull but then that wouldnt explain lack of fuel getting to the carb which I believe you are sure of.

One thing which hasn't been discussed, and usually only happens on a recently rebuilt engine or one with a very bad cooling system. You mentioned that you could turn over the engine, so I don't think this is the cause of the problem, however, I will mention it here just in case.
This problem caused by overheating is expansion of the pistons in the cylinders which will cause the engine to seize until it cools off. This is especially true with aluminum pistons which have a higher rate of heat expansion than steel. If the engine has recently been rebuilt and the piston clearance is too tight this can happen. If it does, the best fix is to remove the pistons and hone the cylinders to get greater clearance. If it is caused by overheating, the fix is to thoroughly clean the cooling system and sometimes even needs a new radiator.
Norm

not a word about vapor lock--i was having a situation very much the same, i found the fuel line was too close to the exhaust pipe, it don't take much with today's warmer temp's and gas that burns hotter to cause this problem, solution --separate the fuel line as far as you can from the exhaust.

In most jurisdictions, today's fuel is primarily designed for use in non-vented, fuel injection systems. It is more volatile than fuel commonly available during the Model T era and it is not intended for use in an atmospheric system. It is more prone to percolation and vapor lock than earlier fuels. Your problem may be related to any part of the fuel system being too close to a source of heat. I used to have access to natural gasoline, which had very high volatility when first collected. The volatile fractions would evaporate over a few days, but when first collected and placed in an overhead gravity storage tank, it could be difficult to get fuel out of the tank in hot weather even when it was full. The total hieght of the tank was about 10 feet, and the oulet to the 3/4" hose was about 7 feet off the ground. In hot weather, fuel would boil in the hose and prevent any flow. The solution was to pour water on the hose and nozzle to cool them off. That's an example of what vaporizing fuel can do as far as defeating gravity flow systems. I've seen a situation where a small dent in a metal fuel line on a 1970s car would cause vapor lock in hot weather when the car was driven a few miles. The pressure drop between the dent and the fuel pump was sufficient to allow the fuel to vaporize in the line when it was hot. Fuel filters located under the hood can pick up a lot of heat and cause problems, especially in systems that lack a pump to hold pressure on the fuel.

Jerry VanOoteghem wrote: ↑

Wed Aug 18, 2021 2:43 pm

Also, check the sediment bulb and its internal screen. If you open the draincock on the sediment bulb, does gas come out? If not, means that you have dirt collected in the bulb such that gas can't pass. Also, may mean that the dirt is piled up as far as the fuel outlet and also blocking the screen.

I really don't think your car being hot has much to do with your problem. It's simply that you don't have enough fuel flow and the engine runs until the carb bowl goes dry. Waiting a while allows it to refill, run another 15 min. & die.

I agree with the above. My '27 did exactly the same thing for the same reason. Unfortunately, the clogged sediment screen was a symptom of a far greater issue - a dirty gas tank. In a '27 the fix is no fun.

He covered vapor lock in his original diagnosis

"I thought it might be a vapor lock problem so I wrapped the exhaust and the fuel lines to shield the fuel from heat. I also made sure the fuel line had a low spot in the middle so any bubbles would go back to the tank or towards the carburetor and not be trapped in the middle. This did not seem to change anything either."

Continued operation could stir up sediment and aggravate a restriction problem. That said, I would not overlook the possibility of heat being a factor. Sediment and fine particles may behave differently when moist as compared to dry. If any water is present, It could contribute to the problem.

I have a 22, on which I had a very similar problem. It has a NH carburetor which I bought at a swap meet. Supposed to have been rebuilt. Upon disassembling the carburetor, I found a grose jet in the float valve. This valve looks like a ball bearing. I installed the typical needle and seat. That fixed the problem. Have you checked yours?
Norm

As the originator of this item, I thought I would let everyone know the changes I have tried and the results....
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After reading all the responses I was convinced it was some sort of vapor lock. Even though I had wrapped the exhaust pipe and shielded the fuel line I was still having problems. Several people stated fuel filters can cause problems that look like vapor lock so I decided that was a good place to start since I had two of them...one in line and a second brass one on the inlet of the carburetor. I decided to start from scratch and return things to the way Henry made them....with a few minor improvements.
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So here is what my system looks like now....I have a brand new fuel line from the tank to the carburetor that has been wrapped in special heat shielding materials and it runs as far away from the exhaust pipe as possible while still running the default factory route. It is fairly flat with a slight dip near the middle so any bubbles will not collect in the middle of the line. The exhaust system has also been wrapped to reduce heat. Everything started well and it ran fine for 15 minutes....the only problem I was running into was low fuel so I drove to the gas station. After I left the gas station I went on a long drive and everything worked fine except for one little stumble on a long uphill grade. It makes sense the fuel filters could have caused this problem because the bottom of the fuel tank is barely above the carburetor so there is very little pressure to push the fuel through. Everything seems fine, but I wish I could have done more testing with a half empty tank. I will keep driving it and let everyone know if the problem returns.

Extra fuel filters are a classic flow problem. Wouldnt hurt to drain some fuel @ the sediment bowl & carb into a clean glass jar eliminate debris questions. Blow back thru the sediment bowl outlet to clear the screen & drain the results.

Does anyone know how the specific gravity of ethanol compares to that of typical pump gasoline?

As I understand it, Montana 500 rules allow raising the fuel tank by about 1 1/2", the idea being to improve fuel delivery. I don't know what modifications to the tank mounting would be necessary to accomplish this, but it's something I'd consider if it did not involve destructive modifications. The procedure would apply to 1925 and earlier cars.

Bryan

I would submit to you that your car is NOT back to the way Henry made it, and to some extent, you are always going to have some stumbling on hills and may have to continue to carry a nearly full tank to get up some hills.

I say this because I have not heard from you, which means you probably did not follow my link, and are likely still running a too-small float valve in your NH.

Scott,
When I said back to the way Henry made it I was saying without filters and a straight through fuel line. I realize the replacement float valves do not deliver as much fuel as they should, but the highest priority problem was the car quitting and stranding me along side the road until it cooled down. That problem has now been resolved.
Yes....I will be buying the upgraded valve very soon, but I am just getting the car on the road and so far the only problem the current valve has given me is one small stumble on a long grade...so it is a lower priority issue that I can address this winter when the snow is too deep to drive it. I appreciate your passion for this issue and it is on my list of things to do.

Thanks....Bryan

It is more fun to drive than walk!

I'm glad you're making progress...have fun on the way!

Check out this thread from 2013. A lot of fuel line routing photos from different angles: www.mtfca.com/discus/messages/331880/35 ... 1366060382. Jim Patrick

I read some discussion somewhere, perhaps on this site in the 2018-back editions, about poor fit with most currently availalable repro exhaust pipes.

Just to update that 2013 thread, I did replace the copper fuel line with steel & used an insulating sleeve. Also, I lagged that stainless exhaust pipe with header wrap. This reduced the cockpit temps for me, a happy result in the hot summer months. There have been zero issues with vapor lock even in very hot conditions.

Paul

In my experience with an older vehicle that would stall when it got hot, similar to your 1914 Model T, I found the root cause to be vapour lock – where the fuel evaporated in the lines from the heat before reaching the carburettor. To resolve this, I insulated the fuel lines more thoroughly and rerouted them away from heat sources. Checking the fuel pump and pipes for wear and damage was also a crucial part of my solution.

These changes significantly improved the vehicle's performance. However, what helped me in understanding and resolving this issue was using a modern tool like https://thingsboard.io/fleet-tracking/. This platform provided real-time data on various aspects of the vehicle's operation, including temperature and fuel flow. It allowed me to monitor the conditions that led to the vapour lock and adjust my strategies accordingly. By integrating this tracking and monitoring, I gained valuable insights into my vehicle's performance, leading to a more effective solution.

Hey OlGeezer..... Nice to see that a newly registered forum member like you is taking the time to research old topics/ posts and to voice your opinion.