Have had some problems with my 78 crew cab and had to have the transmission overhauled. To night driving it across town on the freeway it started surge under a load and going up hills. I had to keep letting off the gas and lower the rpms to stop frog jumping it. I pulled over to the side of the interstate and it idled out ok and didn't stall out but continued to smooth out. I got on it to merg with traffic and after getting it up to almost sixty it came back. Once I got to the exit and took back roads it ran fine with no more problems. I am thinking its a fuel problem. Maybe a dirty filter. I haven't put a hundred miles on the truck since I got it, cause the tranny went out the day I picked it up and it's been in the shop for a few weeks as a friend has helped me out since I sold my house and the garage went with it. The night I drove it to the shop it died on me and I coasted to a parking lot and popped open the hood and noticed there was gas boiling off into vapor in the fuel filter. So that has me thinking it might be vapor locking, but never had it happen so don't know if that's it. Any help you guys can give would be great.

 

Sure sounds like a filter issue to me too. Mine actually had two additional PO added filters that I didn't know about when I bought it. After replacing the stock filter at the carburetor with no luck, I was crawling around underneath and saw more of them tucked up into hard-to-get (of course!) spots.

I've seen the fuel-boil issue in filters as well, but none of them were accompanied by any issues running around. Does seem strange though, but not sure if it's indicative of vapor lock, or something else. Or if it's even a problem at all.
I don't like things that are hard to explain though, so definitely worth checking out.

Could your fuel pump be sucking air through a bad diaphragm maybe? That would explain the fuel starvation symptoms as well.
In fact, the fuel pumps on older vehicles are almost a throw-away item when you buy an old truck like this.
They absolutely hate sitting around for extended periods of time. Whether they're used or even brand new. Especially the brand new ones it seems!

Might be worth a quick test of how good the flow is into a bucket.
A careful test I should say...

Paul

 

I live in South Georgia and my 460 would vapor lock all the time, especially in the summer. I solved my problem with an inline fuel filter that has a 1/4" return line to the tank. I put a tee in the vent line that is next to the filler hose. No more vapor lock. You might check you fuel lines to be sure they are not collapsing and the fuel pump as well. The filter part # Fram G-3583. Hope this helps.

 

Or a WIX 33041.

 

What you describe is exactly, to the tee, what happened with my Chrysler Valiant. I've had the thing since 2005 and probably not changed the fuel filter since then, and it'd just barely cruise at 50mph. Uphill was a struggle, and it was a bit of a slug in general. I put a new generic filter in and it was like a different car.

The problem started after it was laid up for a while, and it sounds like that's the case with you, too. What happens is that the crap in the tank settles to the bottom and gets picked up when you're running, and the old filter (long since gone dry and brittle) collapses and clogs almost immediately.

I prefer to run a simple clear filter before my pump (I run electric on the frame rail near the tank) and then another in the engine bay before the carburetor. Keep a spare in the glove box and you'll be fine.

If you are worried about vapor lock then get some pipe insulation and pop it over the fuel line in the engine bay. You'll notice the difference immediately if vapor lock is the issue as the insulation will block radiant heat as well as insulate against ambient heat. Another basic trick is a carburetor spacer - the phenolic resin type are great for this and I use them on all my builds. As a plus they tend to give you a few more ponies on a well set up system, too.

- boingk

 

Thanks for the advise guys. I popped the hood when I got off work this evening and changed out the fuel filter with a new wicks. I switched tanks before I changed filter as it was on the existing fuel tank. The filter was rust red and as the fuel from rear tank flushed out the bad gas I could see the difference and smell the differnce also.

The guy that I bought the truck from did a number on the crew that's for sure and the fuel line must all be changed from pump to carb. I don't like a rubber hose from pump to carb against hot motor parts. I am going to install a steel line tomorrow morning as I think the rubber fuel line is retiainig more heat on the fuel due to route taken and close to headers. Hope to get it done before a three hundred mile madin voyage to visit family for Christmas. I will pick up a couple of more filters as I might need to switch tanks because gas gauges don't work for either tank and I am unsure of how many miles I can run on the tanks yet. I found four fuses wrapped with cigarette foil wrapper, and more wire spice connectors than should be legal in one truck. I need to get the heater going as well or we're gonna be riding with blankets. I am worried about moving the wires around to much and causing electrical problems before hitting the road after finding foil wrapped fuses.

 

You'll be right - just like they are every second Roadkill episode!

 

If you think your heater core is still good, you might try flushing the coolant system with a purpose-made cleaning solution. This will clear blockages in the heater core that develop from lack of circulation (heat turned off at dash).

Leave the heat turned on at dash until the whole process is finished. Fill the system with distilled water and the cleaner as directed and drive it for 100 miles or so. You will be amazed at the gunk that flushes out the first time. Repeat until you stop seeing a difference what comes out (probably twice, maybe thrice). This fixed the heat on my truck, initially. Then my dash controls went limp, so I'm pretty sure it's time for a new vacuum selector switch now.....

 

Always pays to circulate coolant through the heater core at least once a month. I do it on the way back from filling up with fuel - keeps the core happy and I don't forget.