Short version: What problems do these trucks have with vapor locking, and how can that be solved?

Background & further questions: I bought an '82 F150 with a 351W that wasn't running in my home town in KS. With help from this forum I've sorted the ignition system and have rebuilt the carb, installed a new mechanical fuel pump, replaced all the fuel hoses, and now have dropped/cleaned/reinstalled the tank. Yesterday I thought I had the problems it whipped and could drive it to my shop in OK - about 100 miles.

However, in a test drive at 105 ambient and at between 65 and 70 MPH the temp gauge started crawling up from the O to the M of NORMAL and the engine started bucking - badly. I stopped by the side of the road and could see that the gas coming into the see-through fuel filter was bubbling and turning to vapor. But, the engine ran, albeit with a lot of bucking, so I drove at 45 to 50 back towards my father's house. As I was going up the final hill it bogged, but came back when I shifted to 2nd - only to bog again. I then pulled it down into Low and it made it up the drive.

At that point I guessed that I was using too much black hose from the point where the PO had cut the metal line off just in front of the distributor as I had a see-through filter as well as the metal one on the carb. So, I ran hose straight from the end of the cut-off line to the metal filter, about 6", and also left off the other filter. All to no avail as the engine still bucks.

So, I do have a few questions:
1. Do these trucks have a history of vapor locking?
2. Does it seem probable that this is a vapor locking problem?
3. How has this problem been solved?
4. Do these trucks have a heat riser valve? (The truck is in KS so I can't look 'til I go up again.) If it does and it is stuck shut then......

Help, please!

 

Do you have a spacer between the carb and intake? My understanding is that is to help stop vapor locking.

 

I only have the PCV plate. But, the fuel is vaporizing before getting to the carb.

 

Some Ford trucks have a fuel return line from the engine back to the tank. It's purpose is to keep a the fuel flowing and preventing vapor lock. You may want to investigate to see if the PO disconnected it.

 

General info ...

Something I learned as a kid, anytime a fuel line routes near a heat source from that point on the line needs to slope upwards to prevent vapor locking ...

Sometimes this is not possible so insulation/shielding/rerouting is in need, fuel lines in frames close to exhaust systems ... Kinda hard to keep slopped up from them points!

However, many many times I see fuel lines that run up the side of the motor then down to the carburetor ... That high point is where it'll vapor lock.

Example: Inline sixes are notorious for having the fuel line run up one side of the motor over the rocker cover and down into the carburetor. Major point for vapor locks.

-Enjoy
fh : )_~

 

1. These trucks are not famous for vapor locking.

2. Vapor locking only commonly occurs on the suction line of the pump. Pressurized fuel does not have a tendency to vapor lock.

Does this truck have the stock exhaust on it routed to the pass side?

Do you have the stock metal line fuel running down the driver's side?

I would check the line for rust, and any type of plumbing that may have been to done if it had a dual tank switching valve.

If it's completely stock or the fuel lines have been keep in good shape and routed in the factory location, it should not vapor lock.

 

Thanks to all. Here are my answers/responses/further questions in green:

No one said anything about the heat riser. It's been a long time since I owned a Ford PU, so if you'uns know about this please let me know.

Thanks again!

 

Sorry. The previous response from me looks awful. I attempted to put my responses in the quoted text - to no avail. Please read the stuff between the Color = and the /color commands as my green answers.

 

As for the heat riser, yes I think it has one. If that is stuck closed, it will certainly make the intake get way too hot, as exhaust gasses would be trying to flow thru full time. Of course, I'm guessing you already have an idea what a stuck heat riser will do, since you thought to ask about it's existance.......

 

Also, one silly question. That metal line coming from the pump, does it get anywhere near the exhaust manifold? I have seen plenty of cases where someone replaced the metal line due to breaking it during pump replacement, and they didn't route it far enough away from the exhaust manifold. This could lead to the fuel overheating.

 

I wish I could say, for sure, that the metal line doesn't get near the exhaust manifold, but I can't since the truck is 100 miles away. However, my game plan for the next visit is to check all the fuel line routing, including that line, to ensure it is as far from heat as is possible. Having said that, the fuel pump is far enough ahead of the exhaust manifold that I feel pretty confident that the line, which goes even further forward from the pump, isn't anywhere near the manifold.

As for the heat riser, the factory manual for the '81 truck doesn't show one. And, while that would cause serious heating it looks to me like the fuel is hot long before it gets to the carb.

Gary

 

I fought a vapor lock condition on my truck the first summer I owned it. Turned out, the PO had put one of those universal inline fuel filters on it just ahead of the carb. Being a I-6, that put the filter directly above the exhaust manifold. I moved that filter, and the problem went away. Fuel was visibly boiling inside that filter as well.
That said, I feel your pain, but I think you're on the right track to getting the issue resolved.

 

On my truck, I installed a mechanical fuel pump (epump worked intermittently) and ran black rubber fuel line across the front of the motor and on the front side of the distributor then straight back to the carb to avoid any potential problems. It is run so it gets the cooler air from the fan blowing on it. I have never had any problems with the line run this way, even sitting in city traffic at idle for long periods of time in the middle of summer.

 

[IMG]file:///Users/Lpetralia/Desktop/100_1213.JPG[/IMG]

Here is how I have my line run. I have a 460.

 

I just re-read your post and see you where having the problem at speed. The few times I have had vapor lock with other project vehicles(non-stock) it would not vapor lock going down the road(lots of air flowing around) but would quit on me in town sitting at stoplights.

Generally if you have a fuel delivery problem, the more fuel you use, the more it will aggravate the problem. So sometimes the engine will idle fine, but when pulling a hill or accelerating, it will start bucking.

Another problem that these trucks do have related to heat is the ignition modules. When they get hot, they like to fail, but will be fine when the engine compartment has cooled off.