Big block issues.

[Daddy Classic]

I have a 1969 c10 with a 454 in it. I keep having a problem with it vapor locking. I am running an electric fuel pump in the rear and a Holley mechanical. I am running a fuel pressure regulator with a return line and this hasn't changed anything. Any help would be greatly appreciated.
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[hamjet]

I've never had an engine vapor lock so I don't know what the symptoms are but what is it doing to make you think it's vapor lock?

[LockDoc]

Originally Posted by Daddy Classic

I have a 1969 c10 with a 454 in it. I keep having a problem with it vapor locking. I am running an electric fuel pump in the rear and a Holley mechanical. I am running a fuel pressure regulator with a return line and this hasn't changed anything. Any help would be greatly appreciated.
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My old White '67 had a 454 in it and the gas would boil in the float bowls. Same symptoms as vapor lock. I cured it by putting a 3/4 inch Phenolic spacer between the carb and manifold. You can get them about anywhere any more. Jegs, Summit, O'reilys, e-Bay, etc...

LockDoc

[davepl]

Yeah, the spacer is the first thing to try. We have so much hood clearance that it's not an issue (whereas it can be on some vehicles).

Make sure you have proper steel lines (no more than 6" of rubber in the whole truck) too, and that it's not picking up a bunch of heat under the hood. Lose any glass/plastic clear filters. Ideal is steel line right from pump to carb, with filter in-carb. If running an external filter I prefer the ones you can plumb in with hard line like the factory did.

If you have headers they shed a ton of heat under the hood where don't want it, so coating or wrapping them can help.

The one downside to a return system is you're continually bringing fuel up front, heating it, and returning it to the tank. If you find that it's better when the tank is full (bigger heat sync) maybe you'd be better off with a vanilla fuel system and losing the electric pump? Some people advocate adding the electric pump to cure vapor lock though, so that'd be the last thing I change.

[davischevy]

I don't have your answer, but mine big block was starving for fuel on hard throttle.

My 71 Longhorn with original 402 and Quadrajet seems to vapor lock after sitting at idle such as stoplights drive thru's etc. When I take off It vapor locks if I get in the throttle hard. If I back off the throttle, it will pick and go on.

I changed the pump to carb fuel line with an inline filter. Put an original steel line on it. Put a 3/4" phenolic spacer under the carb.

I raised the float in the Quadrajet and that helped, but It still starves for fuel if it idles very long, creating heat under the hood..



I know none of this helps, but now I am subscribed to the thread.

[swamp rat]

Are ya sure its vapor lock? Non vented fuel cap creating a vacuum in the tank?

[7tee]

I like the ...

1-1" phenolic spacer

2-Fuel lines away from header pipes and hot parts of the engine

3-A vented gas cap

4-Closed up rubber fuel line from the tank to the hard line on frame

5-Stopped up or old sending unit sock

6-Improper carb adjustment

Ed...

[GASoline71]

Running an electric pump into a mechanical used to be the old school way of regulating pressure, so then add another pressure regulator after that and you might have a wonky system that's having issues. What is your pressure set at? What carb do you have? Also... what is your timing set at?

Gary

[davepl]

One way to sort out venting vs vapor lock is when the tank is full and the truck is cold. It should hit a problem sooner (less air space in the tank) with the tank full if it's a venting issue. And when the truck stops, you should be able to hear a hissing sound when you open the cap.

With a return system it'll take LONGER for the problem to manifest with a full tank because it's a bigger heat sync.

Something to think about!

[cla511]

Look at the route of your fuel line. If it's touching anything that carries water you need to move it away from it. I had a 427 vapor lock and the fuel line ran between the block and the water pump. Once I moved it there were no more problems.

[71CHEVYSHORTBED402]

Originally Posted by swamp rat

Are ya sure its vapor lock? Non vented fuel cap creating a vacuum in the tank?

That was my first thought.

[71CHEVYSHORTBED402]

Originally Posted by 7tee

I like the ...

1-1" phenolic spacer

2-Fuel lines away from header pipes and hot parts of the engine

3-A vented gas cap

4-Closed up rubber fuel line from the tank to the hard line on frame

5-Stopped up or old sending unit sock

6-Improper carb adjustment

Ed...

Looks good to me.

[davischevy]

Ethanol blended fuel will vapor lock at lower temp than non ethanol.

[gvw5400]

X2 on the Ethanol blended fuel. I have experienced vapor lock on carbureted trucks that
never had an issue before. All fuel related , the hardware on the engine was all stock.
Don't you love when your government / EPA / Corn subsidies dictate what fuel you can buy. Our trucks are built to run on good old gasoline , not some designer fuel blend made
for a Corolla. All the Best, Dirk

[davepl]

Originally Posted by gvw5400

X2 on the Ethanol blended fuel. I have experienced vapor lock on carbureted trucks that
never had an issue before. All fuel related , the hardware on the engine was all stock.
Don't you love when your government / EPA / Corn subsidies dictate what fuel you can buy. Our trucks are built to run on good old gasoline , not some designer fuel blend made
for a Corolla. All the Best, Dirk

Actually I'm pretty sure Ethanol is about corn which is about getting elected in the primaries. If the first primary were in Seattle we'd all be burning salmon oil. And it burns cool so no vapor lock.

[davischevy]

I email my representatives my opinion of ethanol every now and then.

[67 chevelle]

?

Originally Posted by GASoline71

Running an electric pump into a mechanical used to be the old school way of regulating pressure, so then add another pressure regulator after that and you might have a wonky system that's having issues. What is your pressure set at? What carb do you have? Also... what is your timing set at?

Gary

Agree , Id ditch the electric and run a quality mecanical , with quality filter ,, if that does not cure it ,, id look to vent it ,, or check the vent first , vented tanks should not lock , does the tank gasp when you unscrew the cap ?

[toolboxchev]

Originally Posted by 7tee

I like the ...

1-1" phenolic spacer

2-Fuel lines away from header pipes and hot parts of the engine

3-A vented gas cap

4-Closed up rubber fuel line from the tank to the hard line on frame

5-Stopped up or old sending unit sock

6-Improper carb adjustment

Ed...

Do not forget the fuel pump that will start it when its cold and run under idle, they go bad, and do no pump fuel under partial to wide open throttle.