The vapor lock thread got me thinking I am blaming the wrong thing for my issue.

My '79 with a 400 and manual tranny will cut out sometimes after a 2-3 or a 3-4 shift. It almost dies but usually I can feather the gas enough to get it going again. This only hapens in town as that is when I shift, it runs fine once in 4th and cruising. It has been warm outside recently so I was blaming vapor lock.

I just changed all the plugs, wires, cap, rotor, ignition box, air and carb fuel filters. Got the timing in spec and tuned and cleaned the carb pretty well. Still does it though.

Now I did pull an in-line fuel filter just off the rear tank that the previous owner installed, a large Fram unit. The inlet side poured out rusty gas so it appears the tank is rusted pretty good. It appeared the filter was catching all the rust as it blew out only clean gas when I gave it a little blow. Someone mentioned that they had a rusty filter cause their engine to die, could this be my problem? If so does it make sense that it only dies after a shift and not when cruising? Others are saying maybe a float is sticking in the carb and yet others claim these trucks have bad vapor lock issues.

Pretty confused by the whole cutting out thing, it really stinks to lose all power after a shift in town, all the folks behind me are honking and giving me the bird as they fly around my coasting truck.

 

CO4,
Let's go through some of the basics:
1. How does the vehicle start cold? Does your choke work correctly/ at all?
2. How long does it take to warm up your motor? Does your motor run hot?
3. Once warmed up how does the motor idle? Can you rev up the motor (in neutral) and allow it to come back to an idle without stalling?
4. Is there any backfiring? If so, when and under what circumstance?
Answer these questions and I should be able to give you an accurate answer.
KingFisher

 

1. Engine starts a tad hard when cold, it'll briefly fire right away, then I have to crank it and work the gas for about 5-10 seconds till it fires up. I don't think the choke works at all, it won't idle by itself right away, no fast idle, so I just rev it for about a minute till it idles by itself.

2. Motor takes about 10 minutes to get to full normal temp, doesn't seem to be that hot.

3. Once warmed it idles great. I can sit and rev it and it won't cut out at all.

4. No backfiring at all since I've been driving it.

Hopefully this helps, thanks!

 

I think you found your problem. The rust will clog up the filter and reduce flow. There is also a "sock" filter in the tank and it could be clogged also. I would pull and clean and seal the tank or replace it. Shouldn't have rust.

 

It kind of makes some sense. When you shift gears you take your foot off the gas. Fuel flow momentarily slows, allowing the rust and sediment to clog the filter. Until you feather it and get a good flow again. As said previously, check for any other fuel system filters also.