Carb going dry while driving. Why?
 

My truck has been giving me intermittent vapor locking problems the last few months. I can't figure out why.

Whenever I'm driving at high speed for extended time, after awhile it just starts cutting out. Vapor locking. No gas in carb. Carb is always hot to the touch. I let it cool off for awhile and it always goes back to running normal.

I put a new fuel pump on it, I changed the fuel filters. I'm thinking I should change the rubber lines in case one is collapsing.

I have a 1" phenolic spacer under the carb.


Never used to do this. I could drive it however I wanted to and it was fine.


Why is this happening and what can I do to fix it? Fuel injection anybody???

Could it be because you live in an area that is as hot as the frickin' sun???

Haha!

...I can't tell you why for sure but our 24 Hours of LeMons race truck (a carb'ed 76 Chevy LUV) runs a 2V carb that is equipped with a heat shield (actually an aluminum box with an open top and back) cooled by a 3-inch bilge blower and hose ($40 total) which sources "cold air", okay... at least cooler, and it no longer suffers from vapor lock.

The LUV machine has been dead nuts reliable ever since.... all we do at the track is check the oil, rotate tires, and adjust the air pressure.

You might also check where your fuel lines are in relation to heat sources and insulate them.

Yes on what John said above.
A lot of vehicles run in your climate without your problem. I know you are a smart guy 351 but I suspect that there is an underlying problem that you are not on to yet. Maybe you are in a mind loop chasing a red herring?
Let us know when you solve the problem.

It's Possible. Haha

For some reason though, it's only at higher speed. 75+, for at least 20 miles.

I always ran a 195 thermostat in the truck. I have been considering switching down to a 180, as I've noticed it seems to run better when it's a little bit cooler. Perhaps I will do that and see if that will help

In the good old days we ran clothes pins on the fuel line to combat vapor locking.

You can use Home Depot black water pipe insulation. Looks like hades but works.

At 75 mph the carb is sucking fuel like crazy in these tanks. Maybe fuel delivery just can't keep up.

Just a thought.

Now how in the heck does that work????

Beats me but that's what we all did. Maybe another old guy will explain it.

Is the gas tank venting properly?
Your float is sticking?
Needle is sticking?

If it ran right at some point, and without any hardware changes, you can't start adding in clothes pins and dryer sheets.

I would pull the carb and rebuild it. I am sure having the gas go dry on a hot carb could create some kind of gunk build up that you don't want. At least you could eliminate it as suspect.

Maybe cruise a bit slower? I doubt that is an option?

Tank vents well.
Float/needle/ carb problem? I don't think so. It runs fine at all other times/ conditions.

Run slower???? Ha! Kidding aside, usually I do. 65-70 is average. It will go all day like that.

Why would the thing vapor lock at high speed with all that air blowing over it?
I suggest you look for restrictions in the line from the tank or some such fuel delivery problems.
Clothes pins on the fuel line? Hmm.

I too, have heard of the clothes pins. Never had to try it myself but heard of it back in the day. If you're still running 5/16" line pump to carb I would up it to 3/8". Split some rubber hose and cover the whole line to insulate it from radiator heat. At that speed it's usin' fuel as CJ said. But there's all kinds of Phoenix desert heat made worse by radiator heat hitting that fuel line and carb. Did you ever figure out a fan shroud? A fan shroud would prolly aim the radiator heat more at the front of the motor and carb would get less.

I don't know.


I am running 5/16 line, and I have considered upping it to 3/8. The only reason I haven't is because I like running the small gold filter at the carburetor. And that thing is 5/16. It maybe time that I just do it.

I do have a fan shroud, it's not in the best of shape but it is there.

A 5/16" diameter fuel supply line should easily support 450+ hp. Unless you're making more horsepower than this, probably won't help going to 3/8" diameter line. The problem likely lies somewhere else in the system.