What are symptoms of vapor lock?

[LaOtto70Charger]

Trying to figure out my latest issue.  Starts and runs fine.  No hesitations. No backfire when cold or just warmed up.  I was going 75 no issues.  Than all of a sudden after 20 minutes of driving it started missing and losing power. I backed down to 60 until the next exit and got off the highway to head home.  After away it started acting up 35. Give a little a fuel and missing and some backfire.  It would almost die with full fuel.  Stopped and waited for the wife to come meet me and follow me home.  Buffer cooling she started up fine and drove okay for 10 miles.  Than same thing.  Start missing and backfiring with fuel.  Stop for a minute and idle just fine. Hammer it i. Neutral no issue.  Take off down the road for a bit and cough, sputter, spit.  318 with edelbrock 4 barrel, and points.  Dropped in a rebuilt distributor since mechanical advance was bad. Spark plugs are two weeks old and don't show any fouling or oil.  Vapor lock, bad gas, clocked fuel line, bad fuel pump?  I started buying premium lately and begging to wonder if that ain't it.  So beginning to wonder if it is the issue since I have never had this in the last 23 years.

[Lord Warlock]

may want to see if there is a dirty fuel filter.  When I got vapor lock it was causing the engine to die like fuel starvation, as if fuel wasn't getting much past the fuel pump and it wouldn't let the engine run.  (acted like a blocked filter) I found the vapor canister and yanked it out and plugged up the return line and the car ran fine afterwards.  Probably tossed the OEM canister which I wish I had today just for originality. 

[LaOtto70Charger]

I will probably replace that again.  This actually happened about three weeks ago after I refilled the gas tank.  Just put new champion plugs, wires, points, ballast resistor, etc.. in about week before that.  Filled up just before work.  It coughed a couple times, and than really started acting up after.  All 8 plugs were fouled bad and the filter was actually lose in the clear plastic thing.  Replaced it with a steal one and trying dense plugs.  Along with new carb (found a mixture screw was broken down in deep) and a now the distributor replaced. 

Anyway to inspect those steel filters?

[Kern Dog]

Dirty or rusty gas tank?
I've had the FRAM plastic filters bulge out and when cut opened, I've found lots of flaky brownish stuff in there. Imagine if you didn't have a filter to catch it?
Vapor lock occurs at lower speeds. Driving at 40 or faster should provide adequate airflow to reduce underhood temps quite a bit. I've had vapor lock in my 70 Charger. It has always happened at low speeds as in heavy traffic or parades.
A damaged or failing fuel pump can give you the symptoms you describe too. Running at 75 (Probably 2800 rpms minimum) for 20 minutes will drain a carburetor pretty fast if the fuel system isn't in good shape.

[Lord Warlock]

oh, forgot to mention that it only repeated when car was hot/warmed up, ran fine cold.

[LaOtto70Charger]

Thanks for the input guys.  Fuel filter and pump were making sense.  Temperature part had me going hmmm.  Probably time to at least clean out the 45 year old tank too.

[oldcarnut]

I've got to installed a filter now that the motor is back in.  Anyone know if those work the same before the pump as well as after the pump or is the design made for push through?  Since I got rubber line sections on both sides I'd rather put it before the pump I think.

[LaOtto70Charger]

That's a really good question. 

I have mine right before the carb.  I have a steal line from the pump up the front of the engine to a rubber line.  Than the fuel filter and another rubber line to the carb.  When it was a 2 barrel I had another steel line right at the carb.  That seemed to work fine.  The clear fuel filters are easy to see at least to. 

Not sure what is preferred.

[Kern Dog]

" I have a steal line from the pump up the front of the engine to a rubber line."

Are you worried at all about the cops?   

[68charger440]

 Years ago I had corrosion in my tank that would clog the sock on the fuel sending unit.  When the car stalled i think enough of the crap would fall away without the suction of the pump keeping it stuck to the sock.  Then after starting it again it would suck back enough crap to starve the motor again after a few miles.  When I replaced the tank i think the only thing holding it together was all the crap in the bottom and the sock looked like I tried to strain coffee grounds through it, and my filter was also full of that stuff and I could hardly blow through it.  I have since put a bypass regulator on it and put a filter on the return line also just as an extra precaution because I have had more than my share of fuel problems.  The bypass regulator will also clear out vaporlock issues by keeping cool fuel flowing even at idle in 90 degree stop and go traffic.