84Red

I just recently noticed that my 86 does not have the evap/charcoal canister behind the battery. During the summer, I sometimes had a vaporlock problem where the front tank (maybe rear too but less symptoms) tank would be pressurized enough yo where when taking off the cap would result in an audible whoosh of air rushing in. I also would have hot start conditions where it could take a little while to start. Some people suggest getting a vented gas cap but I have heard that vented gas caps are not really vented. Anyone know where I can find a truly vented dual way gas cap for an 80-86 truck?

84ordF150

Thats a sign that the fuel tank filler neck vent(s) have an issue. My 302 (which i completely rebuilt) has no canister with an open carb bowl vent...no vapor lock.
Vapor lock is a condition where the fuel in the fuel feed line becomes too hot causing air pockets within the line causing a disruption of fuel flow to the carb from the pump. It is not uncommon for the vent tubes to fail due to corrosion issues on the 7th Gen trucks. With a little modification, the 8th Gen filler necks work a lot better.



Midship



Rear

84Red

Where is the actual vent then? Shouldn't there also be a line that goes to the evap cannister? Wouldn't uncapping this like make it not pressurized? I am not 100% sure it is vaporlock, but it is pressurized which is not good. My grandpa was the one who said it might be vaporlock.

84ordF150

Grandpa would be correct if there was not enough pressure in the fuel feed line from the pump to the carb to displace any air pockets caused by excessive engine compartment heat in the summer temps. My 51 Merc did it as well as my 49 DeSoto until i replaced the lines and insulated them from engine compartment heat at lower speeds (city driving). An old school fix we used was to wrap the fuel line in aluminum foil to insulate it.....
(ask Grandpa, I'd bet He remembers it). And you are correct that there should be/was, a vent line from the tank(s) to the missing charcoal canister. It's going to take you getting under the truck near the tanks to find if there is still a vent tube or tubes that were severed when the canister was removed. A line/hose went from the carb's bowl to the canister then from the canister to the tank(s). The canister acted as a vapor storage/exchange for both the carb and tank(s)...if that makes sense. If there is a cut/severed hose flopping around down there, it's my bet that it's full of crud from being open/exposed not allowing pressure from the tank(s) to vent off into the atmosphere causing pressure build up.
Mine vents into the atmosphere. I stuck a A/C schrader screen/valve in the end of the hose to prevent debris from getting in and plugging it up.
Don't tell the EPA...

84Red

So would you suggest a new filler because of the better cap? Or just make the vent line work again?

84ordF150

I should add that the canister also had a purge valve for excess canister pressure
build-up.

84ordF150

I would look for a cut vent hose near the tanks and replace it and use a screen in the open end. Use a few zip-ties to get it up and away from road debris and crud. I use OEM fuel caps on both of my tanks. How is your carb bowl vented ?

84ordF150

Another indication that the "filler neck vent" is faulty is the fuel nozzle at the gas station shuts off prematurely and you have to adjust it's position in the neck to get it to fill.

burnthelight88

Hot start condition could be a completely separate issue. The starters on the late 70's trucks had a heat soak issue, not sure if it extended to 84 or not. The problem is the exhaust passed right by the starter and the starter would soak up all the exhaust heat and cause very slow starts.


My solution was a PMGR starter upgrade. Google it and you'll see its a popular Ford upgrade. Bronco Graveyard sells them for about $70. Its a smaller starter with more torque. I slapped mine on (slight wiring modification necessary, but its done in 5 minutes and the google write-ups are great) and the truck has never started so fast. I highly suggest it.