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Vapor lock?

Daniel Foster

Daniel Foster

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Hey guys. I have a 1968 Charger with a 383 and I’m trying to solve a mystery. Once the car is fully warmed up, about 195-200, it doesn’t like to idle. The car will die repeatedly in traffic at a standstill at idle if I don’t put it in neutral and feather the throttle. The car starts up immediately when it dies. The weather has been 75-90. It also does I’m the morning when it’s significantly cooler, 60ish. I haven’t driven the car for long distances or in traffic until the summer heat set in so I can’t say if this is a new problem or not. The carburetor is an Edelbrock 1407. Mopar electronic ignition. I tested the fuel pump and it’s putting out just over 7psi. Fuel lines are steel up to the pump and 3/8 rubber to the filter and carburetor. I use Chevron or Shell 92 gas. I haven’t noticed any other performance issues other than dying at idle. I’ve looked around for a definitive test to determine if it’s really vapor lock but didn’t find anything conclusive. Is there a way to test for vapor lock? Any other ideas as to what it could be? Float levels?
 
What is your timing? You can always bump it up a few degrees to raise the idle and add a few more in/hg of vacuum.
 
threewood said:
What is your timing? You can always bump it up a few degrees to raise the idle and add a few more in/hg of vacuum.
Click to expand...
Agreed, use a vacuum gauge when you set your timing, advance until you get the highest reading and stop. If the car starts there, you are probably right on. Set the timing first then adjust your idle mixture screws to again reach the highest vacuum reading. Eliminate these first and if still having an issue you may have a more complicated problem. I assume you are running a stock or near stock cam, if that's the case it should idle at 850-900 rpm
 
It sounds like you are running the exact same thing as I am, except that mine is a 1411, and I have no such problems.

It would seem to me, if it where a vapor lock, it would not restart so quickly, not to mention that the temps you posted are no where near vapor lock territory. When I first bought the car it had a 190 thermostat (unbeknownst to me) and no fan shroud. It once got to 230°, but it never vapor locked.
Unless your fuel line is strapped to your exhaust pipe, I'd doubt it is a vapor lock.

The car will die repeatedly in traffic at a standstill at idle if I don’t put it in neutral and feather the throttle.
Click to expand...
I agree with the other guys. Sounds a lot like too low of an idle (or possibly a vacuum leak?)
 
Last edited:
Yeah, I've had A LOT of vapor lock issues & when it happens, the engine does not start up right away (since the carburetor is dry). You "might" double check to see if your fuel line is running really close to your exhaust, but I don't think that's it either. Maybe swap out your in-line fuel filter just for the heck of it & follow the other guys' advice above.
 
Daniel Foster said:
Hey guys. I have a 1968 Charger with a 383 and I’m trying to solve a mystery. Once the car is fully warmed up, about 195-200, it doesn’t like to idle. The car will die repeatedly in traffic at a standstill at idle if I don’t put it in neutral and feather the throttle. The car starts up immediately when it dies. The weather has been 75-90. It also does I’m the morning when it’s significantly cooler, 60ish. I haven’t driven the car for long distances or in traffic until the summer heat set in so I can’t say if this is a new problem or not. The carburetor is an Edelbrock 1407. Mopar electronic ignition. I tested the fuel pump and it’s putting out just over 7psi. Fuel lines are steel up to the pump and 3/8 rubber to the filter and carburetor. I use Chevron or Shell 92 gas. I haven’t noticed any other performance issues other than dying at idle. I’ve looked around for a definitive test to determine if it’s really vapor lock but didn’t find anything conclusive. Is there a way to test for vapor lock? Any other ideas as to what it could be? Float levels?
Click to expand...

I am having the exact same issues, and it's very frustrating when your slowing to a stop sign or etc. not to mention embarassing. I have put another carb on there and no issues with it, the car works great with the new carb.
On the old carb, and the new, the pressure is reading 6 lbs. all the time that it is wanting to stall, so that is telling me that the fuel is good up to that point, ruling out the fuel pump or filter and leading it to the lines going into the carb or the carb itself.
I will admit thou the new carb is set for a higher idle comparing from the old one at 800 rpm to 1100 rpm with the new. It will be interesting to see what it comes down to. I really hate to buy a new carb,
I'll try to keep you posted.
 
Im no carb pro , but I don't think edelbrocks work well with much over 6lbs of fuel pressure. if you are over 7lbs it may be pushing to much fuel past the seats and over filling the bowls.
does have a strong gas smell when its acting up ?
 
The car does smell of fuel when it acts up. It also smells of fuel after it has sat over night. The vacuum gauge read 7.2 psi. Is 1.2 psi enough to cause a problem?
 
Daniel Foster said:
The car does smell of fuel when it acts up. It also smells of fuel after it has sat over night. The vacuum gauge read 7.2 psi. Is 1.2 psi enough to cause a problem?
Click to expand...

7.2 vacuum at idle? Stockish cam? That sounds pretty low. Do you know what your timing is set at? Check for a vacuum leak around the carb, maybe a loose or cracked vacuum advance hose or rubber cap on a carb port.
 
Threewood gives good advice about the vacuum caps. Mine had a crack that was only visible when I squeezed it hard. Had intermittent rough idle.
Just an fyi my 383 has 15 inches vacuum at idle, timing advanced to slightly off the scale, and idle is 800 rpm. My fuel pressure is slightly over 7.
Keep us posted.
 
Daniel Foster said:
The car does smell of fuel when it acts up. It also smells of fuel after it has sat over night. The vacuum gauge read 7.2 psi. Is 1.2 psi enough to cause a problem?
Click to expand...
are you saying 7.2 psi of fuel pressure or 7.2 inches of vacuum?
 
Try looking in the carb when it stalls. See if you see fuel dripping into the intake. If so, it's probably flooding. If you don't see fuel, pump the throttle, while looking in the carb. No fuel, that's where to start.
Also, no one mentioned adjusting the fuel/air screws. When idling, turn them out, slowly, alternating back and forth to get the highest vacuum, or rpm. Then reset idle. This is done after timing is adjusted correctly.
 
After everything else is checked and set:
Another tip, always adjust the idle screws at operating temperature. I go a little less than 1/4 turn closed (clockwise or lean) after I've reached max RPM. It really doesn't affect idle quality and helps prevent fouling on rapid deceleration on a decline.
But be careful for that cooling fan!
 
Also if it only does it when the car is good and warmed up it may be fuel boiling in the carb bowls. I ran into this as did many of my friends in Maryland where I live running the 92 pump gas. The pump is not like it used to be years ago when all cars had carbs. Now they are all fuel injected from the factories and they can run this crap pump in fuel injection cars without any problems. The best thing I found to fight fuel boiling was to add a 1inch phenolic or wood spacer under the carb. It made a big difference in helping on my car. You can just see the phenolic spacer I use on my eng under my carb. You cant use a metal spacer because it wont help as it will still transfer the heat to the carb. The wood or phenolic wont transfer the heat to the carb. Ron

413957239.jpg
 
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