Vapor lock

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Mountainrider
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Vapor lock

Post by Mountainrider » Wed Sep 11, 2019 10:28 pm

Do T,s vapor lock. Or did my float stick close for a few minutes and engine died. Got out, cranked it and it restarted and the rest of the 10 mile drive home was uneventful. Up and down some steep hills no problem.


DickC
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Re: Vapor lock

Post by DickC » Thu Sep 12, 2019 1:15 am

Yes. There are several posts on this forum concerning vapor lock. Most deal with the routing of the gas line near the exhaust pipe. I have found that my 1912 will have a problem on real hot days and early afternoon when on a tour with the club. I have found that when we have driven far enough in the morning that the tank gets down to 1/2 or less there isn't enough pressure in the gas line to overcome the vapor lock. If I have a fuller tank, I never vapor lock.

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Humblej
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Re: Vapor lock

Post by Humblej » Thu Sep 12, 2019 8:35 am

Neil,
A gravity flow fuel system with an under the seat tank does not take much to restrict flow to the carb. A sticky float valve, crud in the line or tank or sediment bulb or carb, low fuel level, fuel line routing, fuel line size, fuel line kinks, fuel tank vent blockage, loose blob of fuel valve lube, carb float adjustment, road surface temperature, the alignment of the moon and stars, or running over a homeless bum sleeping in the street can do it or contribute to it. I think of vapor lock as being more a problem for a fuel pump than a gravity feed system. My first go at this problem would be to check for a physical restriction which is most of the above mentioned maladies.


Norman Kling
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Re: Vapor lock

Post by Norman Kling » Thu Sep 12, 2019 9:10 am

A helpful hint is that from the lowest point in the fuel line, it should go uphill at both ends. If you have a spot in the line which is higher than the ends, the vapor will rise to that spot and compress which will keep fuel from flowing, but it goes uphill at both ends from the low point, the vapor will go either back to the tank or to the carburetor and be expelled. With the below seat tank, it is always good to start a tour with a full tank and judge your distance between gas stops so that you keep it over half tank. This is especially true in hilly country.
Norm


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Re: Vapor lock

Post by Scott_Conger » Thu Sep 12, 2019 11:23 am

Vapor lock is indeed a real thing. However, I believe that much of what is blamed on vapor lock is a problem that manifests itself when on hilly drives or traveling at a higher than normal rate of speed. If you are running an NH carburetor that may very well be a float valve which is manufactured wrong and does not have proper through-put. This requires the tank to be much fuller than necessary to provide the "oomph" to get the fuel into the carb through the small hole (9 gallon hill) and will cause the car to run quite hot on long hard pulls or at higher speed due to fuel level drop in bowl resulting in leaner mixture. This will become a self-regulating problem as you will never be able to go faster than the fuel will pour into the bowl. "Surging" is another example of the lean-correct-lean-correct filling of the bowl. You run well until mixture is wrong, car falters, fuel refills, you're good to go, and so on.
Scott Conger

Tyranny under the guise of law is still Tyranny

NH Full Flow Float Valves
Obsolete carburetor parts manufactured


Norman Kling
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Re: Vapor lock

Post by Norman Kling » Thu Sep 12, 2019 11:56 am

I have found that the needle and seat float valve works much better than a Gros valve. Also float level makes a difference especially for climbing hills. The float should be just about straight across and level with the pin to the opposite side. The manual on Carburetors will tell you the exact setting for each type of carburetor. If the level is too low, it will run fine at moderate speeds on level or downhill but when going uphill it will seem like you are running out of gas. If you slow down and give it less gas, it will run more smoothly. When the float level is set right, it should pull most hills if you have enough gas in the tank.
Norm


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Re: Vapor lock

Post by Scott_Conger » Thu Sep 12, 2019 5:53 pm

When the float level is set right, it should pull most hills if you have enough gas in the tank.
This is an entirely acurate, simple and direct statement, whose meaning is surprisingly indeterminite, and really, there's the rub...how much gas in the tank is enough? With a restricted float valve, there are several hills around my dad's house which required 7-8 gallons for his heavy hack to climb. With that restricted valve replaced with a freer flowing one, he climbs those same hills easier and quicker, plus he isn't overheating at the top, with barely 1/2 tank.

There is a reason they call it a fuel system. In a system, the sum of the parts must be correct and any one error/fault means the end result will be compromised.
Scott Conger

Tyranny under the guise of law is still Tyranny

NH Full Flow Float Valves
Obsolete carburetor parts manufactured


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Mountainrider
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Re: Vapor lock

Post by Mountainrider » Thu Sep 12, 2019 9:26 pm

Been doing steep hills no problems. This happen after a long gentle down hill keeping speed around 30-35. My T does 30-35 with out pushing it. I’ll pull the the Holly G and make sure there is no crud. Weird it started right back up and gave me no more trouble all the way home.


Scott_Conger
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Re: Vapor lock

Post by Scott_Conger » Thu Sep 12, 2019 11:44 pm

Could have been nothing more than a bit of fluff caught up in the jet and you'll never have a problem again. Wouldn't be the first time.
Scott Conger

Tyranny under the guise of law is still Tyranny

NH Full Flow Float Valves
Obsolete carburetor parts manufactured


Norman Kling
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Re: Vapor lock

Post by Norman Kling » Fri Sep 13, 2019 11:08 am

There is a hill near here that I can climb in the 26 with Ruckstell and Low. I don't usually climb that hill because there is another way around not so steep. I wouldn't even attempt to climb with the 22 even with a full tank. The reason I don't like to go that way in the 26 is because of gravity flow oil system. The front of the engine would be starved for oil. In any case, if the level of gas in the tank is lower than the carburetor, you will not be able to go up going forward unless you have either a pressurized tank or a fuel pump. Of course that difference will vary with the car. The worst for climbing hills is the car with the tank under the rear seat. The best would be the 26-27.
It is very unlikely that you will find hills in New York state as steep as the ones in Southern California.
Norm


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Re: Vapor lock

Post by Scott_Conger » Fri Sep 13, 2019 11:26 am

Norm

don't dismiss the Hudson River Valley or Adirondacks and Catskills for challenging roads. You don't need jagged rock formations to have serious climbs.
Scott Conger

Tyranny under the guise of law is still Tyranny

NH Full Flow Float Valves
Obsolete carburetor parts manufactured

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Ruxstel24
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Re: Vapor lock

Post by Ruxstel24 » Fri Sep 13, 2019 1:52 pm

I've been experiencing some issues after a good run and a hard pull uphill...I had already blew out the line and the sediment bowl.
After reading this thread, I rechecked my fuel line and unhooked it, found a piece of heat shielding from an old wiring harness. Slid it up the line covering the closest to the exhaust pipe.
I also realized the fuel level was too low, on the Stromberg OF, and raised it up to the proper level (I think... :lol: )
It made a big improvement, hasn't missed a beat since, after a quick readjustment. :D

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