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1977 W100 Dies after 25 minutes

2K views 13 replies 6 participants last post by  Powerwagon77 
#1 ·
Hey guys im new to the forum, I recently purchased a 77 powerwagon club cab short bed with 400 4barrel ,eldebrock 625 carb, longtube headers. Once we got the truck home we fired it up and it started first crank, we were all standing around it when 15-30 minutes later it shut off like someone turned the key. I would try to fire it up right after it died and it would refuse to start. Any ideas? Hopefully a bad ground or something. Please let me know I don't know much about these all trucks, however, they are badass.:gr_patrio
 
#2 ·
Check for spark at plugs: if none, check at dizzy, then coil (ballast resistors on firewall? is one common issue; carry a spare in glove box). ... Would be wise to do amp gauge bypass (tons of info on this); this link did a 76

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

... If spark is good, check for fuel (or prime thru carb with a bit/tad of fuel to see if it will fire or "try" to run); beware of flashbacks thru carb when priming. ... Welcome, and good luck!
 
#6 ·
Vapor lock is a conditon created by the fuel line becoming hot enough to cause the gasoline inside of it to become vapor. This effictively shuts down the liquid gasoline from reaching the carburetor. No gas in the carb = no running engine.

If you suspect this to be the case, re-route the gas line to the carburetor and try to increase some airflow in that area. Sometimes this can have a great influence in keeping the fuel line cool enough.

I second the suggestion to do the amp gauge bypass if it has not already been done.
 
#8 ·
To be clear, this is not about the engine overheating. It is about the engine bay not having enough (cooler) air flow and getting (locally) hotter than the vapor point of fuel (about 450 degrees?).

If the truck is moving - or pointed into a good wind - it will stay cool enough under the hood so the gas will not vaporize. The same thing can happen if you get the engine hot and then shut off the truck. The heat soaks in (and there is no flow of cooler fuel) and after a short time the fuel in the line vaporizes.

Check that the fuel line is not running close to the exhaust system or touching the block. Grady
 
#10 · (Edited)
Powerwagon77 said:
Ok man hopefully all this shitty weather goes away
With this "shitty weather" quote and a "snow on the ground" avatar, if vapor lock is the issue it's likely to become a bigger/huge problem in spring/summer. ... Everyone gave you good advice.
... "Metal large ish" fuel filters absorb heat and transfer it to the fuel, ditto for metal lines etc; insulating them may help (slit lengthwise hunks of old "rubber" rad/heater hose, or use bicycle tubes, orrrrrr$); the lines before the pump may be the biggest problem (pump can't suck bubbles/vapor).

... Is shroud in place, and fan properly spaced; and careful "where" you cardboard/cover rad if you do in winter.

... Others may have advice about gasket for carb to intake (insulating and/or phenolic); have seen somewhere 400 with heatshield to protect carb from intake "crossover passage" heat.

... If it still has vapor lock issues: consider covering outside of fuel pump with a layer of silicone(do not plug the vent hole, it must remain open).
 
#11 ·
I recently purchased a 77 powerwagon club cab short bed with 400 4barrel
Is this the motor that came in the truck? It wasn't a swap from a small block was it? If so the radiator will be to small and cause overheating. After i rebuild my motor it still had issues with vapor lock and it would run hot. Replaced the original radiator with a nice three row and never had vapor lock/high temps again.:)
 
#12 ·
Original big block, & are u sure it could be vapor lock? How does the motor get that hot in such a short amount of time? I personally believe its something electrical but of its not that then ill assume it would be vapor lock.
 
#13 ·
Vapor lock was one suggestion and a good one, but it is only one suggestion. Someone else mentioned spark. The coil could be getting hot and not firing. Verify fuel to the carb after the truck shuts down by removing the air cleaner lid and looking down the throat of the carb while you open the throttle all the way. You should see fuel squirt. If not it may be vapor lock. If the bowls do have fuel, then remove a spark plug wire from the plug and insert a phillips screwdriver into the wire end where the plug was. Using the plastic handle (you don't want to touch the metal part), hold the metal shank of the screwdriver about 1/4 to 1/2 inch away from the header tube while someone cranks the truck over. You should see a strong blue spark between the screwdriver and the header tube.

Try both of these out and get back to us. Good luck.
 
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