A couple years ago, I had the '79 Bronco 400 in for a routine tuneup/oil change/etc. The shop noticed a small fuel leak at the short rubber flex connecting the rigid fuel line to the fuel filter at the carb and replaced the rubber connector.

Since then, the engine has failed a few times, usually when accelerating. The symptoms were like 'out of gas' or 'failing ignition module' and only in hot weather. On one occasion, after taking the few minutes to replace the ignition module, it started right up, ran smoothly a few seconds and quit again.

From the start, I figured something was heat sensitive.

The other day, I popped the hood and noticed that the rigid fuel line was hard against the water outlet on the manifold. I loosened the hose clamp on the rubber hose attaching the rigid line to the fuel filter and pushed the rigid line further into the rubber hose. This separated the rigid fuel line from the water outlet by about an inch and a half.

Question: was this vapor lock, and could it have been caused by the hard contact between the rigid metal fuel line and the water metal water outlet on the manifold?

I haven't had vapor lock problems since I visited my '49 Merc with clothespins!

 

It was vapor lock.

 

You can avoid vapor lock entirely with a hot fuel return system.

Ford used a system on the 460 in 80's vans.

You can make one with a tee at the carb and a 1/16" dia orifice in a return line plumbed back into the fuel tank.

 

Well, so far, so good. With the '89/302 Bronco in the shop, I've been driving the '79/400 Bronco to town. I've been doing it in the afternoon, the hottest time of day, and so far, no hiccups!

The first mystery of the Universe: How long do you wait for an intermitent thing not to happen?

 

Had the same problem in a 79 F150, 400 cid, but without that rigid fuel line. Problem I encountered was fuel that had methanol added to it for pollution control (Albuquerque, NM @ altitude 5200 feet, ) and then only in the heat of the summer. They add methanol to the gasoline there during the winter. Couple of the chains just keep the same gas year round. Use that stuff during the summer and the methanolated vapor locked in about 10 minutes.

 

Hadn't heard of that. I've seen signs at pumps that say this-or-that is or isn't added. If I understand the gasoline distribution system, selected additives are mixed in when delivery is made to individual stations.

I'll have to keep my eyes open.

 

Torque1st, I understand all you said about the hot fuel return except "and a 1/16" dia orifice". What are you referring to in regards this part?