Vapor Lock
 

What causes vapor lock and how can I prevent it? I already have fiberglas braiding on the fuel line as it comes up over the block. 350 V-8 3.y.o.crate engine in '71 4x4 Jimmy sm465 tranny. City driving, hot day and a tank of fresh "Environmentally Correct" 87 octane name brand gas. After about 25 miles of errand running in city traffic, the engine started running rough, "burble-ing" and then cut out on me completely. I pulled over -- could see nothing unusual under the hood. It would turn over, catch and die, then just turn over. I called "Roadside rescue" on my cell phone and they told me there was a 1 hour wait. After an hour and 15 minutes, I tried it and it started right up again and I got going under my own power a block before the puzzled hook driver got there. Ran Ok for the rest of the day. Go figure?

When my truck Vapor Locked on me, it never ran rough but it would just cut out on me and Die!! When I had a problem w/ my ignition module in my HEI, when the module would get Hot and shut down, my engine would run rough because it was having a weak spark and then it would shut down.. After about 30 min - 1.5 hours, it would start up and run Rough for about 10 minuets then it would run fine untill the Module Heated Up and shut off again.. Talk about a PITA, I drove around for about a week thinking that it was Vapor Locking, then one night I drove out and it did the same thing and lucky enough I had my dad and a small screwdriver w/ me to check spark!! I replaced the Module the next day and never had a problem since!!

Also if you are sure it is Vapor Locking, then answer a couple of Questions for me. What kind of Fuel Pump are you Running ?? Are you Running Headers ?? If you are using a Mechanical Fuel Pump and Headers, Switch to an Electric Fuel Pump and put the Fuel Pump as close to your gas tank as Possible! If you are running an Electric Fuel Pump, do you have it installed in Engine Compartment ?? Well the solution is move electric fuel pump in the frame rails as close to the Gas Tank as possible.. Headers can really cause Vapor Lock, if you have mechanical fuel pump or electric fuel pump in the engine compartment!! Trust me on this subject because I burned 2 electric fuel pumps up because of the heat problem and I had my fuel pump in my engine compartment! (It took me 2 weeks before I learned to move my electric fuel pump underneath my cab in the frame rail.)My truck vapor locked every time I drove it to town untill I moved my fuel pump!!

Vapor lock occurs when the vapor pressure of the fuel is higher than the surrounding environment. In older engines with "sucking" fuel pumps at the engine the pressure in the fuel line to the tank is reduced by the sucking action of the fuel pump drawing fuel form the fuel tank, and when heated, the gasoline actually boils creating a vapor of gasoline which the fuel pump can not handle, thus the name "vapor lock".
More than likely if it did vapor lock it was becasue of the headers or exhaust pipes. If it keeps happening try rapping the pipes.

'68OrangeSunshine, I had the same problem this Summer!!

When I ran the truck on CNG, I never had a problem with vapor lock, lol...probably because CNG IS a vapor, but it was a life saver! Better than sitting in heat, stuck on the side of the road, with vapor lock! When I ran the truck on gasoline, that's exactly what happened!! I was curious though, as my fuel line going to the pump is laying flat against the engine block, is that right?

When I first assembled my engine into the truck I carefully bent a new fuel line from the pump to the carb, taking my time, making it just right. fit it right up close to the block, heads and intake manifold, looked great, but after a 1/2 hour of driving it would bog down, as though it was starving for fuel. I figured "vapor lock" and bent up a new line giving it plenty of clearance (aprox 2") and it never did it again.

The set-up is a 350 crate motor: (about 25,000 new) SM465, Carter AFB 600cfm, Weiand 8004 intake, Heddman Hedders, Mechanical fuel pump -- [Stock AC Delco]. Fuel comes from stock blazer tank in frame aft of differential. HEI ignition. [Cannibalized unit from my previous ride, a '67 Sub K/10 w/454.] Replaced all distributor components about 3 years ago. Maybe module's gone bad. It's a cheap enough fix.Had a similar problem 2 years ago when hedders were burning up plug wires (ignition would cut out when under load and hot), went to white fiberglas braid wraps around plug terminals and hi-temp silicon wires. Same jacketing is on fuel line coming up from pump to inline gas filter [G15]. Fuel line runs about 1 1/2" from block.
My buddy rode shotgun with me today when we went to get my 292 block back from machine shop. I thought I heard the pre-burble and got his attention. He said he thought he heard a "whistling" from engine bay. Manifold, headers, collecters? Could be there -- I wouldn't hear it after 4 years around high pitched jets in my misguided youth.Could burned out header or collecter gaskets contribute to this effect?