68 chevy truck problems

[homersipes]

My friend has a 68 chevy truck with a 350 and when it gets hot it dies like it starving for fuel.  He has pulled the fuel line off of the inline fuel filter and the fuel was quite hot and it fired right back up kinda acts like it vapor locks.  This only happens in hot weather as he lives in Tuscon Az his morning commute is cool and it dont effect it, but his drive home when the weather is hot this happens.  Any ideas???  cool can? if anyone has heard of this.  any suggestions would be nice. 

[Melvin]

Does it have the original mechanical fuel pump or did he replace it with an electric jobby?


When's the last time he monkeyed with the carb?


When's the last time he set the timing?


When's the last time it got a tune up?


Bad gas?



When my truck acts like a beeyotch, these are the questions I ask myself.



EDIT: Check all fluids and then start on the mechanicals. Just my opinion. Surely CAP1 will be along to set us straight.

 

[homersipes]

he did a tuneup when he bought the truck cap rotor plugs and wires, hasnt messed withcarb not sure what it is for a carb and has the original mechanical pump.  I kinda hit a brick wall when he told me it only does it in the afternoon when its hot, if he lets it sit for 10 or so minutes it will start back up.  My original thought was the vent on the tank but he said when he takes the cap off it doesnt hiss.  Yeah I am sure cap will be along and have an idea

[Buzzard7]

Sounds like vapor lock. What carb does it have? Cap will correct me if I am wrong but timing should be 6 before TDC.

[icepac]

Doesn't the stock fuel line run right against the water pump?

I've seen guys changing the small filter on the carb accidently bend the line so it touches the pump and having that problem afterward.

I've also see guys replace the super thick gasket with a thin one which causes the carb to get hotter than with the thicker one.

Exhaust leak blowing directly on the line or pump body?

Flapper stuck closed causing all exhaust from one bank to have to transfer through the intake manifold to the other side?

The newer formulations of gasoline are less resistant to vapor locking and it's gotten worse in the last 3 years.

[morfiend]

Doesn't the stock fuel line run right against the water pump?

I've seen guys changing the small filter on the carb accidently bend the line so it touches the pump and having that problem afterward.

I've also see guys replace the super thick gasket with a thin one which causes the carb to get hotter than with the thicker one.

Exhaust leak blowing directly on the line or pump body?

Flapper stuck closed causing all exhaust from one bank to have to transfer through the intake manifold to the other side?

The newer formulations of gasoline are less resistant to vapor locking and it's gotten worse in the last 3 years.

  Yup some excellent ideas,sound like the fuel is boiling in the carb,too much carbon build up could also be an issue.

     I'm surprized the 68 runs on unleaded fuel to begin with......


   

[Melvin]

Doesn't the stock fuel line run right against the water pump?

I've seen guys changing the small filter on the carb accidently bend the line so it touches the pump and having that problem afterward.

I've also see guys replace the super thick gasket with a thin one which causes the carb to get hotter than with the thicker one.

Exhaust leak blowing directly on the line or pump body?

Flapper stuck closed causing all exhaust from one bank to have to transfer through the intake manifold to the other side?

The newer formulations of gasoline are less resistant to vapor locking and it's gotten worse in the last 3 years.

It's not a Lambo dude.


Fuel, spark, air.








oh wait...

[SFRT - Frenchy]

As Icepac mentioned, you can never go wrong with a 1" phenolic carb spacer ... but are you really sure your problem is the fuel boiling? I say that because I'm not sure if the engine is warming up the fuel, a few degrees more of outside air temperature really matters. As an example, my 72 Dodge has the fuel line sitting on the intake manifold and rubbing against the heater coolant line. It does not affect the driving, but when I start with a warm engine I have to depress the gas pedal, otherwise no go. But I have to do that no matter the outside air temp, winter or summer here in Utah.

I don't thing it's timing related either again for the same reason hot bad/cold good. Too advance and u'll ping on hard accelerations, too retarded and you'll take off like a bat out of hell to sputter/loose power 50y later.

Is it dying at idle in traffic, or while driving down the road? When it dies, does she restarts while craking AND holding the gas pedal WOT?

What type of choque do you have on this carb? Manual? Electric? Automatic? Maybe the thing malfunctions?  ... Do you have an aftermarket electronic ignition? I had an older module once that didn't like being in a corner of my engine compartment and was "overheating/acting up'. 

[homersipes]

these are all good ideas to start, I will have to call him again tonight when I get home for some more info. thanks for the help gents.

[Shuffler]

The carb spacer is where I'd go first. I see it has already been suggested.

[Grayeagle]

My Duster had same problem .. fenderwell headers put too much heat into engine compartment and vapor locked the carbs big time.
I could not go anywhere without lettin it sit for 10 minutes or so before firing it up again.
This *with* half inch fuel line into the fuel log and 3/8" line to each carb bowl and a steady 6lbs of pressure.

I put a cool-can in, problem gone.
It was a cork lined can about the size of a coffee can, aluminum tubing wrapped inside,
..fuel inlet on the bottom and out the top, installed after the fuel pump,
mounted up front away from the heat.
Made by Moroso.

Later, when I went to a tunnel ram the carbs were out in the breeze
and cool can was not required.

Only car I ever had the problem with.

-Frank aka GE

[CAP1]

My friend has a 68 chevy truck with a 350 and when it gets hot it dies like it starving for fuel.  He has pulled the fuel line off of the inline fuel filter and the fuel was quite hot and it fired right back up kinda acts like it vapor locks.  This only happens in hot weather as he lives in Tuscon Az his morning commute is cool and it dont effect it, but his drive home when the weather is hot this happens.  Any ideas???  cool can? if anyone has heard of this.  any suggestions would be nice.  

 does he have the original mechanical fuel pump? how about the carb? which one? what kind of filter, and how is its condition? if he has a clear filter, and he's vapor locking, he should see air in that filter. when running, it should be about half way full. if it dies due to vaporlock, it'll be empty. the pressure with the original mechanical pump should be about 5psi max., on a stock carb.

 if he suspects vapor locking, he's gonna have to insulate the lines with heat wrap.

 also, even though you think it's in the fuel area, check point dwell, and ignition timing. someone up the thread mentioned 6 BTDC, which i believe is the spec for a 68 350. i used to run mine at 10 though. it just all around ran better. check dwell FIRST though, as changing dwell will change your ignition timing. dwell for this engine should be around 31-32 degrees at idle. more means your point gap is too big.....less means your point gap is too small. increase gap, decrease dwell, decrease gap, increase dwell. hopefully , he put new points in when he did the cap/rotor/wires. and hopefully, he lubed the lobes on the shaft.

[TwinBoom]

if it original motor he should be running lead additive so he dont muck up the valve train

[F22RaptorDude]

I'll tell you what the problem is... Its not a Ford 

[CAP1]

I'll tell you what the problem is... Its not a Ford 

 come to think of it....that would be one helluve cool ride if he swapped a coyote 5 liter into there.