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Old 09-09-2019, 03:49 PM
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possibe vapor lock issue

I have a basically stock 74 c10. I drove it to work and back twice with no issue. About 20 min each way. A few nights later i drove it roughly the same distance and when i put it in park it died. Went to start it a few hours later and just turned over. Held the throttle wide open and it finally started. Got home no problem. Same thing keeps happening though. I have a clear filter i can see through. So i let it run and after 10-15 min the fuel level drops and goes to almost empty then it dies. First thought was the pump diaphragm was bad so i changed that. Didnt work. Rerouted the fuel line cause it was touching the headers. Now its 6 inches away with a heat sheild. That didnt fix it. Tried running off a gas can incase there was an issue in the fuel tank but the same thing happed. Then i hooked a vaccum gauge to the pump and that read good. Today i insulated the line from the pump to the carb but still no dice. So does anyone have an idea why theres a sudden loss of fuel once the engine is hot? Also its very hard to start or it wont restart at all while its still hot. Im stuck on this one. Thank you to all for any advice on this.

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Old 09-09-2019, 03:56 PM
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I chased this same issue on a 440 Charger one time, the fuel pump pushrod was worn down about 3/16" and was decreasing pump output. Is it possible your camshaft pump lobe could be worn? Ethanol gas makes this worse, the vapor pressure is higher.
A problem with the vent on the tank might also do this, try opening the cap when it suits off.
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Old 09-09-2019, 05:43 PM
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I would hope the camshaft isnt worn down. It has less than 50 miles on it. That pump rod is most likely original though. Ill try running it without the cap first though. Thanks.
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Old 09-09-2019, 06:03 PM
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The carb on my car boils the fuel away after sitting for a while.

One way to check is drive it, then let it sit overnight, next day after, pop the air cleaner off and work the throttle, see if any gas squirts out, if not, there is a big part of the problem, gas boiling out of the carb.

If gas boils just in the fuel line alone, usually what's left in the float bowl or bowls will let the engine idle long enough so the pump can push the vapor out and let fresh fuel in and off you go, having no clue anything is wrong. Most carbureted stuff runs for a minute or 2 before driving anyway.

Does your truck smell rich when idling after it's warmed up? Could the fuel pump be overpowering the needle and seat if it's new, parts store pumps are known now to put out more pressure than a carb is supposed to handle.

Use to, having to hold the throttle wide open meant it was flooded and had to clear out.

Do you have any yellow gas stains on the intake, means an external leak.


Furthermore, what carb, fuel line size, and fuel pump do you have.
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Old 09-09-2019, 06:40 PM
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Well it did it with the old pump too but just recently. Had the truck a few years and never had this problem. Im using 3/8 line. Its got a 650cfm 4 barrel holley carb. The pump is just some regular pump from the parts store.
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Old 09-09-2019, 06:41 PM
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I had a 1967 Rochester Q-jet and it did the same thing as you described.

I removed the little bronze filter in the carburetor inlet and installed a in-line Fuel filter and that fixed it. Those bronze filters in the carburetor inlet wil not pass moisture and will stop up with a little condensation in the fuel system.
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Old 09-09-2019, 06:45 PM
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Already have an inline filter so that base is covered
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Old 09-09-2019, 08:12 PM
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Ok chuck that plastic filter into your trash bin.
They are good for making sure you have fuel and that is it.
Things crack, rupture, or the screen can rip over time. They are a huge fire risk.

Run a aluminum inline filter with a stainless screen. $40-60 well spent and they can be cleaned easily by basically flushing them with gas in the opposite direction in which they are normally run for 5 mins before reinstalling.


You need to let the thing sit overnight then do the squirt test above by pulling the intake and seeing how much if any fuel comes out.

If you have fuel. Fill the floats with stable wait a night.
This helps free up debries. In order to do this you start the truck and hold the throttle around 3k for 10 seconds then let off. This forces that ethanol goop out of the system.

Let the engine cool for a hour then do a "second treatment" with carb cleaner "fuel injectior" cleaner(additive) filling the floats again.

Wait 3+ hours for it to break down the goop then do another full throttle start holding it at 3500 for 10 seconds, let the thing idle(bet it idles better) and then take it for a drive.

With these newer engines you almost need to run some kind of cleaner like stable every couple of tanks(around 60 gal) to keep things clean.
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Old 09-10-2019, 09:06 AM
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What carb is on it?
I've done a hell of a lot with heat related fuel problems and believe I know a good deal about the subject. Some may disagree?
Anyway it sounds like two different fuel problems.
1) The fuel boiled (percolated) in the carb, flooding it.
2) The fuel is boiling in the line giving you the symptoms you see in the filter.
Or a 3rd, the fuel boiled in the line after it was shut down, raising the fuel pressure and blowing fuel past the needle and seat in the carb and flooding it.

For the carb the first and easiest thing is to add a 1" insulating spacer. If it's still a problem then blocking the exhaust crossovers may be needed. My car has both done, and if I'm driving on a day when it's over 85, when I get home I still have to raise the hood to keep it from boiling in the carb.

For the vapor in the filter, get it good and hot in the driveway until you see the vapor getting bad. Take a garden hose and run water over the fuel pump. (give it a minute) If the vapor goes away, you can start by running a fuel return line back to the tank with a bypass regulator. This will keep the fuel flowing 20X faster and possibly stop the pump from having enough time to boil it. I did that and it fixed mine 95% of the time. If it still does it, then you may have to change to an electric pump.


The gas these days has too much butane in it which boils by itself at 32 (ethanol is a tiny factor and buying ethanol free fuel will show you that the problem will most likely still be there.) Different locations in the US have different fuel standards, specifically the REID vapor pressure. More and more older cars are having this problem. After I ran an electric pump with a return line someone showed me a link to a youtube video from a speed shop. They did the same thing. And if you search on youtube, you will find a lot of video's now showing the same thing. If they keep lowering the standards for fuel, we will all have to go to fuel injection someday.
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Old 09-10-2019, 09:32 AM
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Dodge 440 cars in the 1960's had fuel filters near the carb that had a orifice and fuel return to the tank to help with vapor lock, this is not a new problem.
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Old 09-10-2019, 01:09 PM
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Same thing here with my 68 Ford Fairlane except mine does it while idling in a drive thru after starting it after a hot soak

Tow it home, starts next day. Glad I got AAA. This has happened twice in 20 years so it's not like Everytime I drive it. Just tends to happen unexpectedly.

One thing I found was the tubing going from the pump to carb was touching the water pump. Which might be acting as a heat sink.

Thinking of going to an electric pump.
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Old 09-10-2019, 08:36 PM
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So where would i hook into to run a return line? I am going to get a spacer for the carb. Ive touched the fuel pump and that isnt even hot. I am most likely going to change to electric though. About 8 inches up the line from the pump is where it starts to warm up. Ill try the fuel treatment too. It just confuses me that ive had this truck for three years and never had this problem til this summer. i dont know what the difference is suddenly.
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Old 09-11-2019, 06:41 AM
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Quote:
Originally Posted by lmsport View Post
Dodge 440 cars in the 1960's had fuel filters near the carb that had a orifice and fuel return to the tank to help with vapor lock, this is not a new problem.

No, not a new problem, but it does seem to be getting more prevalent.
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Old 09-11-2019, 07:03 AM
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Quote:
Originally Posted by fedtrucker View Post
So where would i hook into to run a return line? I am going to get a spacer for the carb. Ive touched the fuel pump and that isnt even hot. I am most likely going to change to electric though. About 8 inches up the line from the pump is where it starts to warm up. Ill try the fuel treatment too. It just confuses me that ive had this truck for three years and never had this problem til this summer. i dont know what the difference is suddenly.

Easiest place for the return is usually to weld a bung onto the fill tube. That would be when the tube is not installed in the car! I can't say why it suddenly acted up but most likely a different formulation of the gasoline. What fuel treatment? I missed that. If you have a low compression engine you can add some kerosene to raise the boiling point, but I don't think many of us here have low compression engines. (the kero lowers the octane rating)
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Old 09-11-2019, 09:44 AM
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As mentioned, the filler tube will be fine. I will add it probably wouldn't hurt after you get the filler tube off and away from the truck to wash it out, let it dry some, wash it out, then give it the test with a grill lighter. Can't be too careful with gas and welders.

If you aren't in any danger of needing this truck for a daily driver, wait through the winter and see if it quits. Allegedly, gas formulas change and the colder weather will knock stagnant heat down quickly. See if it quits then.

One good thing about an electric pump is it will run when the key is switched on vs having to turn the motor over, pushing any fumes out of the way and refilling with gas.
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