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  #16 (permalink)  
Old 03-16-2009, 04:41 PM
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Quote:
Originally Posted by 40forddgc
Certainly something that could be possible. Could the pump lose pressure when it get hot. When it craps out its always when the road conditions are hot.

Not sure if ambient temp can affect the pumps performance but if it's weak, it can't overcome air bubbles from the vapor lock as easily as when it's pumping properly.

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Old 03-16-2009, 05:24 PM
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clothes pin

Quote:
Originally Posted by moontanker
Use cclothe pins on your fuel line ,works like majic.
Actually I was always told to use a piece of aluminum foil about 6", just C fold it over the fuel line & clip it with a clothes pin. It probably was enough to catch some air & cool the line, that's the only explanation I could guess.

AND YES IT HAS WORKED FOR ME ALREADY!
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Old 03-16-2009, 05:34 PM
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...use a piece of aluminum foil...
I hadn't thought of that for years!

OT, but when we'd get a car that came to our yard (Tom's Auto Salvage, St. Cloud, FL ca. 1960- '75) that had tin foil wrapped around the fuel line, we knew to be suspect of the carb. Usually they were found with assorted trash in them, plugged filter and/or sugared carb guts.

We didn't even bother w/them.

I think this must be the first empirical evidence I've heard, that it actually did anything. Thanks.
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Old 03-16-2009, 06:24 PM
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Your problem does not sound like vapor lock. Vapor lock used to happen on a hot day with a real hot engine compartment. You would shut the car off, the fuel would vaporize in the line and the vapor pressure would keep the fuel from flowing to the carb. The old fuel pumps generally didnt have as much pressure as the modern ones. Sounds more like a float level or pump issue, or you are loosing spark. Just about everything is affected by temperature.
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  #20 (permalink)  
Old 03-17-2009, 11:03 AM
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vapor lock

It seems to happen on a hot day under load. the engine temp is normal. After it graps out for a second or two all of a sudden starts to run fine again.
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Old 03-17-2009, 11:07 AM
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Vapor Lock

Sounds like dirt, water in fuel. Seems like more and more folks are seeing this problem come up lately. I see it everyday in small engine applications where the machine is not used daily.

The machine runs for awhile, but after running a short distance, mostly after they stop and then try and accelerate, the engine farts, skips or quits. The cause is usually bad fuel, water.

I know you all know this already, but heck, let me say it one more time. Water is heavier than fuel. When you get gas at the station the water is agitated into the fuel and as long as you run the machine everyday the water stays encapsulated within the gas. If you allow it to sit for a few days the water begins to seperate and settles to the bottom. The good stuff goes to the top,right?

Depending on how bad the ratio of fuel to water is, you might run for awhile and then get a good drink of the crap into the engine and it will skip or die. With a warmed up engine the water, liquid, in the heat will turn to a gas and when you try to crank it again it may start and then run again.

Also depending at what time of year the gas was put in, you may be suffering from the winter mix blues. Winter mix fuels are generally loaded with additives to prevent fuel line freeze and to adjust the explosion for cold temps. When the weather warms up and you try to run this fuel the additives cause it to flash off too fast and then ka-pow the engine dies.

Hope this helps.
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Old 03-17-2009, 02:26 PM
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vapor lock

That sounds pretty damn close to what i am experiencing....however it happens on long runs with fresh fuel...What can be done if anything?
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Old 03-17-2009, 09:26 PM
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My experience was same as Jmarks. If my Olds 350 idled for more than a couple of minutes the fuel pressure would gradually drop from 6 psi down to zero and the engine would die. New fuel pump solved the problem. A pressure gauge between the pump and carb helps diagnose this problem.

John
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Old 03-18-2009, 09:27 AM
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vapor lock

It happens when I have driven long distances of an hour or more and all of a sudden it craps out going down the freeway or getting off the freeway stopped... and then as I take off it craps out. If I let off the gas and pump it a little it comes back to life and is OK again.
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Old 03-18-2009, 01:48 PM
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Quote:
Originally Posted by 40forddgc
What would cause vapor lock and how can I prevent it? Engine is a 383 Chevy, with a 750 Holey. It seems to happen on hot days. When it happens the engine is at normal operating temperature.

thanks
Vapor lock is common with engine mounted mechanical fuel pumps or electric pumps mounted a distance forward of the fuel tank. This puts fuel from a distant tank under reduced pressure in the feed line to the pump. Combine the reduced pressure in the line with heat of a hot day, the pressure and temperature of the fuel in the line can be arrive at a point below the fuel's Vapor Pressure. When that happens the fuel changes state from a liquid to a gas the latter state can't be pumped by the pump and the carb gets starved for fuel.

Certainly fixes that either keep heat from the fuel line or allow the line to sink heat from itself to someplace else will help keep the fuel from vaporizing in the line.

Modern fuel injection systems use an electric pump near to or in the tank because electric injectors are not tolerant of operating without fuel to cool them. So relocating the pump by or in the tank keeps the fuel line pressurized which raises the vapor pressure point keeping the fuel from flashing to vapor in the feed line. You can do the same thing with an electric pump by or in the tank to feed a carb. You don't need the mechanical pump if you do this and you need to keep pressure at the carb close to a max of 6 psi which might need a regulator. My preference is a return regulator if the pump is outside the tank as the return fuel can be tee'ed into the line ahead of the pump, this keeps a continuous flow of fuel going thru the pump which helps keep it cool, this adds a lot of life to the pump. You can return fuel back to the tank if desired, but for tanks not designed for a return this can be a PIA to plumb.

Bogie
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Old 03-18-2009, 02:22 PM
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vapor lock

Thanks. My fuel pump is located within a foot of the gas tank. I do have a pressure gauge mounted in line by the carburetor. Last time I checked at an idle it was 7PSI. Why would this problem occur only after a long cruise on a hot day?
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Old 03-18-2009, 03:38 PM
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Quote:
Originally Posted by 40forddgc
Thanks. My fuel pump is located within a foot of the gas tank. I do have a pressure gauge mounted in line by the carburetor. Last time I checked at an idle it was 7PSI. Why would this problem occur only after a long cruise on a hot day?
I hate it when things lead back into the problem. Some people responding to your question posed the possibility that the problem was other than vapor lock.

And I wasn't trying to say it was vapor lock, just pointing out how vapor lock happens.

Your response to that defines a system that doesn't sound like it's necessarily one that sees vapor in the lines issues so long as the pump is at least level with the bottom of the tank. Most rotary or piston style electric pumps are not self priming although this state is perhaps laced with a lot of circumstantial evidence that they can keep up on some self prime. But generally, if the fuel level gets lower than the pump's impeller they can starve themselves.

Moving in another direction which other contributors have touched upon is electrical. That begs the question of what is the ignition system?

Bogie
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