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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #1 ·
Sorry for the continued new posts, slowly learning this engine and carbureted engines in general.
Replaced mechanical fuel pump this week. Old one had a bad diaphragm, would not pump out of the pressure side with good fuel supply.
Today, after making more carb adjustments, the pre-carb fuel filter was almost empty again. Shut the truck off and checked the fuel supply, it was okay. The pressure line had air pressure, almost like an air lock. Relieved it and primed the fuel system, worked fine, but then it did the same thing again. I removed the fuel line from the tank and also the pump, and blew it out with compressed air. All clear. Re-primed and started, same issue cropped up minutes later. The fuel flow from the tank seems okay at times and then other times it’s more air than fuel. No breaks in the line and the tank has at least 10-12 gallons (likely more).

I have installed a new fuel filler cap, and there was a homemade vent line on top of the tank (pressure vent attached to 3/8 hose). I plugged the hose end thinking it was the source of my fuel leak the prior week, most likely was the fuel sender oring. Could this vent being plugged be my issue? For what it’s worth, I ran the truck again with the fuel cap off and it did the same thing.
 

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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #3 ·
Is there a fuel sock/filter on the pickup in the tank?
There is a sock over the pickup tube. It appeared clean when I pulled it last week to replace the gasket between the sender and the tank. But I wasn’t super focused on it at the time. Might be worth looking in to at this point.
 

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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #4 ·
I think I’ve figured this one out. It’s been about 7 hours since I last cranked the truck, it’s about 15 degrees cooler out now. Cranked and fuel pressure was all there. I’m thinking I have a vapor lock due to fuel boil at the pump. Going to look into a fuel vapor separator to hopefully cure this issue.
But it makes perfect sense, I don’t seem to have an issue unless I’m idling in the driveway after letting the engine run for half an hour (maybe longer?)
 

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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #6 ·
If it’s an “all stock” setup you shouldn’t have an issue with vapor lock. I’m not saying it’s impossible but usually vapor lock happens at high ambient temperatures.
It should be mostly stock if not all stock. I’m definitely still learning this 77 F100. Sender, fuel lines and pump are all what I would call stock. Right now, I’m running the engine in the driveway trying to get the mixture screws dialed in on the carb, and also letting it idle freely just to get things up to temp and just watch what’s going on. Better to have a problem in the driveway than miles from home. Since there’s no air flow due to the truck sitting still, and the high heat, I’m thinking it’s gotta be the fuel boiling.

Going to install the vapor separator and probably some heat shield wrap for the fuel lines just to hopefully help prevent a problem down the line.
 

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The 1977 Ford truck shop manual says the mechanical fuel pump on the 460 engine in the F series should produce 5.0 - 7.0 P.S.I. with the temperature normalized, at idle, in neutral. The minimum volume flow should be 1 pint in 20 seconds.
 

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HI If you think you have vapor locking.. follow you fuel line form the carb to the tank and is if it gets to close to exhaust , headers. or even going over engine if it crosses any part of the exhaust it can cause vapor locking..
good luck
tim
 

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Discussion Starter · #13 ·
Hey guys, for some reason my notifications weren’t going to my inbox, so I missed some responses.
I installed a vapor separator filter between the fuel pump and the carburetor, and kept the clear in line filter ahead of the carbuertor. Keep in mind I’m running rubber fuel line basically from the tank to the pump (there are a couple of metal lines along the frame) and then rubber line from the pump to the separator, and again from the separator to the inline filter and carburetor.

took the truck out for a longer test drive around the neighborhood, so low speeds and some stops. Definitely have a timing issue (engine knocks when giving a lot of gas going uphill), but I got back home and let the truck idle in the driveway for a few minutes. I noticed the gauge for the fuel pressure, mounted on the fuel line for the carburetor, was reading 0. If I pinch the vapor line, the fuel pressure gauge comes up. Is there something I’m missing? The clear fuel filter seems to fill up with vapor again, something I thought was corrected with the separator. There is heat tape on the fuel line from separator to the carburetor.
At this point, I’m about to heat-wrap the entire fuel line from the tank to the pump. If that doesn’t work, I guess I’m looking at doing an electric pump at the tank. At least I already have a return line plumbed just in case.
 

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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #14 ·
Went back out to take a look at the engine bay temps roughly 45 minutes or so after shutdown. Still pretty warm with temps no more than 150.
Started taking pictures of the fuel setup when I realized that the rubber line from the tank to the pump was running about 6 inches away from the headers. Stupid me didn’t even notice!
I plan on wrapping that line in heat tape to hopefully correct the issue. Otherwise like I said in the previous post, it’s probably time to convert to an electric pump
 

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HI ??? I've never heard of a vapor seperator for the fuel line???? are you sure your not confusing the fuel return line on the one line in and two lines out fuel filter?? as a separator??

good luck take care be safe
tim
 

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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #16 ·
HI ??? I've never heard of a vapor seperator for the fuel line???? are you sure your not confusing the fuel return line on the one line in and two lines out fuel filter?? as a separator??

good luck take care be safe
tim
hey Tim, so there’s one fuel line from the tank to the pump. Then one line from the pressure side of the pump to the separator (it’s an off brand Wix filter). Then off the top of the separator, there’s two lines, one goes to the carb, the other is the vapor return line that I ran back to the fuel tank.
 

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Discussion Starter · #17 ·
A vapor separation system would be a band aid. Fix the issue, protect the pump and lines from heat, or increase the pressure and run a regulator.
Arnold, what could I do about protecting the pump from heat? It’s just a standard mechanical pump, so not sure how I would go about protecting it.
 

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A good place to start is to ensure all of the proper shrouds are in place. Second, look at DEIs catalog, they sell all sorts of things to protect critical components from heat. How old is the pump? Check lines for cracks, as route everything away from heat.
 

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1977 F100 - 460 from a 1969 Lincoln, C6 Trans, 9" Rear
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Discussion Starter · #19 ·
A good place to start is to ensure all of the proper shrouds are in place. Second, look at DEIs catalog, they sell all sorts of things to protect critical components from heat. How old is the pump? Check lines for cracks, as route everything away from heat.
Excellent, thank you! Definitely no shrouds which is likely another cause for the heat under the hood. The electric fans are mounted to the radiator, and there are no heat shields for the headers other than the fiberglass heat wraps. The pump is brand new, installed earlier in March. I’ll go back over the rubber lines between the tank and pump since those haven’t been replaced, and take the time to wrap the lines with heat protection tape.
 
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