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1984 F150 300/4sp 4x4. This is my yard/plow truck and up to now has been pretty reliable. I run it maybe 2x 3x a week so it doesn't sit long. I let it sit for a solid week last month, got in, tried to fire it up, and no gas to the carb. Replaced fuel pump, old one was known bad (NO suction at all) and problem solved. I let it sit for another week without using or starting it and--same thing! I pulled the line from the fuel pump, had a helper crank it and it's getting great suction (enough to hold your finger to the hose while cranking. Bypassed the fuel tank and hooked up a fuel line to a gas can and placed on the fender. Fired right up. Replaced the bypassed hose back to it's proper feed (the fuel tank) and no problems for about another week. Today-same issue!
It *seems* like the fuel wants to settle back to the tank after not running it for awhile. This almost seems too much for the fuel pump to pull. I checked pump again and there's good strong suction.Any idea on what's going on here?
1984 F150 300/4sp 4x4. This is my yard/plow truck and up to now has been pretty reliable. I run it maybe 2x 3x a week so it doesn't sit long. I let it sit for a solid week last month, got in, tried to fire it up, and no gas to the carb. Replaced fuel pump, old one was known bad (NO suction at all) and problem solved. I let it sit for another week without using or starting it and--same thing! I pulled the line from the fuel pump, had a helper crank it and it's getting great suction (enough to hold your finger to the hose while cranking. Bypassed the fuel tank and hooked up a fuel line to a gas can and placed on the fender. Fired right up. Replaced the bypassed hose back to it's proper feed (the fuel tank) and no problems for about another week. Today-same issue!
It *seems* like the fuel wants to settle back to the tank after not running it for awhile. This almost seems too much for the fuel pump to pull. I checked pump again and there's good strong suction.Any idea on what's going on here?
Before condeming the new pump I would pul the sending unit and check the pick up screen to make sure it is not plugged up. If it is clear then you may have just a got a bad pump.
85 probably has blue plastic soft lines between pickup right up to hard line before pump. No idea how well those hold up. I would drop tank and check out pickup sock screen as well. Make sure fuel tank vent(s) are clear.
I have a 1986 F150 with 4.9L engine and Carter YF carburetor. The engine has been converted to Duraspark ignition. My son has a 1984 F150 with 4.9L engine which still uses the stock feedback ignition and Carter YFA carburetor. Both are daily driven and when driven everyday, start immediately. However, since the advent of gasohol, both, if allowed to sit for approximately a week, both engines require extended multiple attempts to get started for the first time, but start normally thereafter.
I have a 1986 F150 with 4.9L engine and Carter YF carburetor. The engine has been converted to Duraspark ignition. My son has a 1984 F150 with 4.9L engine which still uses the stock feedback ignition and Carter YFA carburetor. Both are daily driven and when driven everyday, start immediately. However, since the advent of gasohol, both, if allowed to sit for approximately a week, both engines require extended multiple attempts to get started for the first time, but start normally thereafter.
My 81 F100 with the 4.9 / 300 six does the same thing. When it was cooler I was driving it every day to work and it would fire right up.
Now that is has gotten hotter and no AC in the truck (yet), it sits for a week. I use it to take the trash to the dump as it has the permit other wise it sits.
I do have to crank it a lot before the gas refills the carb and it is fine after that.
Dave ----
If you leave the large emissions vent port open on top of the carb, it tends to let the fuel evaporate out of the carb bowl faster. I plugged it off and the cranking problem after sitting a couple of weeks went away. But if you plug it off, it tends to make the engine hard to start when it's hot. You can't seem to win with that port, on my old 84 Bronco I hooked it back up to the solenoid and the charcoal canister. That got rid of the raw fuel smell also when it was hot outside.
If you leave the large emissions vent port open on top of the carb, it tends to let the fuel evaporate out of the carb bowl faster. I plugged it off and the cranking problem after sitting a couple of weeks went away. But if you plug it off, it tends to make the engine hard to start when it's hot. You can't seem to win with that port, on my old 84 Bronco I hooked it back up to the solenoid and the charcoal canister. That got rid of the raw fuel smell also when it was hot outside.
I cant remember how I have it ATM as I was doing some testing of the EVAP system to see if it was a cause of the low MPG but then I added the over drive soI will have to start the testing all over.
Dave ----
OK, here's a quick follow-up...I pulled the sending unit out & inspected it. It was clean and unobstructed. Lines are fresh,too I forgot to mention that. However, while looking at the carb I found a crack at the base of the carb spacer. Would this cause the evaporation issue that Franklin2 mentioned? Anyone have an idea on where to score a new (or good used) one?
That looks to be, on phone so hard to tell, the EGR plate.
That would not cause any evaporation but could cause a vacuum leak.
There is a "for sale" area down farther could check there maybe ask in the 240/300 motor area if someone has one after they did a v4 manifold and carb swap.
Dave ----
I cant remember how I have it ATM as I was doing some testing of the EVAP system to see if it was a cause of the low MPG but then I added the over drive soI will have to start the testing all over.
Dave ----
It looks like your EGR adapter plate has been modified. That is an aluminum piece and can be repaired by welding. A few are available on eBay:
What I am talkign about is the large open pipe to the right of the fuel inlet on the single barrel carb in the picture below.
And it Tee's into the canisters under the battery and vacuum is pulled from the PVC with some other valves in place for when the EVAP system is to work.
Thing is I don't have the other valves so when ever the motor was running vacuum was pulling on the bowl vent & canisters.
If it was pulling fumes it could make the motor run rich and why I am getting poor MPG.
With that and now not driving the truck much, to damn hot & no AC, I don't know what all is going on but so far I can live with it and when I get time will check some things.
Dave ----
Pulling a vacuum on top of the bowl may actually make it run lean. It's atmospheric pressure pushing down on the fuel in the bowl is what makes the fuel go through the jets and through the venturi into the engine. Putting vacuum on the bowl may lessen the pressure in the bowl. I have never tried that though, I always used the solenoid valve. It's closed during running, open when not running. And gasoline fumes are heavier than air. So they require the line to go downhill to the solenoid, and then keep going downhill to the canister. That's why the canisters are mounted so low in the engine compartment. When the engine is off, the solenoid is open, and any gas fumes in the bowl and also in the carb throat/aircleaner area flow down through the lines and into the charcoal canister.
Pulling a vacuum on top of the bowl may actually make it run lean. It's atmospheric pressure pushing down on the fuel in the bowl is what makes the fuel go through the jets and through the venturi into the engine. Putting vacuum on the bowl may lessen the pressure in the bowl. I have never tried that though, I always used the solenoid valve. It's closed during running, open when not running. And gasoline fumes are heavier than air. So they require the line to go downhill to the solenoid, and then keep going downhill to the canister. That's why the canisters are mounted so low in the engine compartment. When the engine is off, the solenoid is open, and any gas fumes in the bowl and also in the carb throat/aircleaner area flow down through the lines and into the charcoal canister.
You can't pull a vacuum in the bowl through the evap port as the bowl is vented, this applies to ALL auto carbs. We have covered this many times before about the fuel bowls having their own separate venting apart from the evap port. See below bowl vents circled on the Holley and the Carter.
Having a constant vacuum with high enough flow on the evap vent MAY affect fuel-air mix the higher the temp of the carb the more of an impact this will have as the Fuel will be able to evaporate faster. It should NOT affect fuel economy as you would have been burning this fuel vapour one way or another if not pulled in from the evap vent it would have spilled out from bowl vent.
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