Vaporlock issues help.....

[BIG ORANGE]

I'm sure this has been covered but I could get through the search feature,
70 model truck is vapor locking after high heat a some time setting in traffic.
Original tank is clean, new fuel sender, new fuel pump, new fuel filter and new gas cap.
I can see the gas bubbling in the filter. Also I've noticed alot of back pressure anytime I remove the gas cap too. Any advice on the matter?
I appreciate it guy's......

[68 P.O.S.]

Which carb do you have? Which fuel pump? What's your timing set at?

[BIG ORANGE]

Qjet carb Delphi pump from Napa, not sure on the timing question. Truck runs like a top until it got hotter temps here lately.

[body bolt]

I have the same problem with my stock (except for HEI) '71 C10 350/350. I've also replaced the pump and used a phenolic spacer as an insulator and an insulator under the carburetor. I've found cooling the pump by running water over it improves the idle but obviously not a solution. I'll be adding a Carter P4070 electric pump to push fuel through the mechanical pump. If that doesn't fix it I'm going to fuel injection. My truck has had this problem since I bought it in '98 and I've decided I've had enough.

[Steeveedee]

Are you guys running the AC? And what is the water temp, if you have a gauge?

[Barnfind46]

If you guys live in an area that only has fuel with 10% ethanol then that may be the problem. The ethanol lowers the boiling point if it is not under pressure. I had to wrap my fuel line and reroute the metal fuel line by the engine block. That helped but then I added an electric fuel pump. The pump is rated at 7 psi. Any more and your carb may flood when the fuel pushes past the needle & seat. That made a huge difference. I lived in Dallas/ Fort Worth and drove in traffic every day. When the temp was up close to 100 I would still have a little problem but my truck tends to over heat in traffic when it is that hot. Now I live in Arkansas and have access to ethanol free fuel. hope this helps.

[Willys_MB]

You can get a vented gas cap. HEI failure also mimics vapor lock. Food for thought

[BIG ORANGE]

Originally Posted by Steeveedee

Are you guys running the AC? And what is the water temp, if you have a gauge?

No A/C and the temperature on the gauge is normal, the truck isn't running hot at all.
There was a elderly guy said to place a few wooden clothes pins on the fuel line from the pump to the carb. He didn't know the idear behind that but says it works in some cases.
I thought about using those heat restitic hoses that goes over sparkplugs.
Aslong as your just out driving the truck runs fine, but don't try stopping fr a period of time in traffic or waiting long in a drive through fr something to eat.lol
Should there be so much back pressure on the gas cap, its suppose to be vented.

[RustyPile]

Originally Posted by BIG ORANGE

No A/C and the temperature on the gauge is normal, the truck isn't running hot at all.
There was a elderly guy said to place a few wooden clothes pins on the fuel line from the pump to the carb. He didn't know the idear behind that but says it works in some cases.
I thought about using those heat restitic hoses that goes over sparkplugs.
Aslong as your just out driving the truck runs fine, but don't try stopping fr a period of time in traffic or waiting long in a drive through fr something to eat.lol
Should there be so much back pressure on the gas cap, its suppose to be vented.

Clothes pins?? Is that old wives tale still circulating???? The best solution that will not create excessive fuel line pressure is a slight "redesign" of the fuel lines and fuel pump.. Install a later model "3 port" fuel pump.. The extra port is for a return line.. You'll need to use 1/4" steel fuel line.. Route the line back to the tank and connect it to a fuel sending unit that's designed for a return line.. This setup keeps the fuel circulating back to the tank and doesn't allow heat buildup that causes vapor lock...

As for that gas cap.. Either the vent hole is plugged or it's simply not a vented cap..

[Steeveedee]

Originally Posted by BIG ORANGE

No A/C and the temperature on the gauge is normal, the truck isn't running hot at all.
There was a elderly guy said to place a few wooden clothes pins on the fuel line from the pump to the carb. He didn't know the idear behind that but says it works in some cases.
I thought about using those heat restitic hoses that goes over sparkplugs.
Aslong as your just out driving the truck runs fine, but don't try stopping fr a period of time in traffic or waiting long in a drive through fr something to eat.lol
Should there be so much back pressure on the gas cap, its suppose to be vented.

My truck has a "vented" cap, and blows off more pressure than I would like. There's a thread on here about reducing the pressure. I'm considering doing that change to mine.

[body bolt]

With or without A/C and 205F at the outlet with an IR thermometer. The Duke City gets warm in the summertime.

Originally Posted by Steeveedee

Are you guys running the AC? And what is the water temp, if you have a gauge?

[BIG ORANGE]

Originally Posted by Steeveedee

My truck has a "vented" cap, and blows off more pressure than I would like. There's a thread on here about reducing the pressure. I'm considering doing that change to mine.

Hey Steve,
Would you attach that link in a thread so I could read it please.
Thanxs

[Caddylackn]

Originally Posted by RustyPile

Clothes pins?? Is that old wives tale still circulating???? The best solution that will not create excessive fuel line pressure is a slight "redesign" of the fuel lines and fuel pump.. Install a later model "3 port" fuel pump.. The extra port is for a return line.. You'll need to use 1/4" steel fuel line.. Route the line back to the tank and connect it to a fuel sending unit that's designed for a return line.. This setup keeps the fuel circulating back to the tank and doesn't allow heat buildup that causes vapor lock...

+1 on a fuel return line. Heat soak in the fuel line becomes critical if the fuel is barely moving, like at idle in traffic. The slow moving fuel has more time to suck up heat and boil. The lack of air movement also enhances this. You can wrap the fuel line to the carb in one of those reflective foil type of wrap insulation and that will help. A return fuel line to the tank will solve this problem. You can add a fuel pressure regulator with a return line fitting and run a new line back to the tank or you can run a mechanical fuel pump with a return line. This will keep the fuel circulating and cool. Starting in the mid to late 70s GM started putting in fuel pumps with the return line fitting in their vehicles to prevent vapor lock.

Excessive fuel line pressure will actually help prevent the fuel boiling, since the boiling point of gasoline fuel is dependent on the pressure. The lower the pressure the lower the boiling point. Fuel injection rarely has vapor lock for two reasons, there is a higher operating fuel pressure, and there usually is a return line to the tank.

If you are running headers, the added heat in the engine department and the close clearance between where the hard fuel line and the header cross at the frame can definitely increase your chances of vapor lock. You can either make a simple heat shield for the metal fuel line by the frame to protect it from heat from the header or wrap your headers.