celcius232

New-old Ford owner here--I recently picked up a cherry 1984 F-150 Supercab 4x4 long bed garage queen with 56K original miles. It is a loaded XLT model with the 351HO motor, cruise, AC, PS, PB, C-6 automatic, and limited slip 3.50 rear end. It also has the trailer towing package and high altitude emissions for here in western MT. The motor was virtually untouched and had all the original belts and hoses and all massive amount of emissions equipment is intact. I change out the leaking fuel pump after the 100-mile 14 mpg drive home, along with the belts (cracked) and, dist. cap, rotor and Autolite 25 plugs. Around town driving revealed horrible mileage (less than 5 mpg) and black soot blowing out of the pipes on startup. Also the cold weather (below aout 30F) driveablity is awful and the the engine stumbles and hesitates badly until fully warmed up. If I plug in the block heater it is a bit better than stone cold. I put a new carb kit in the Holley this weekend and I noticed it had been done at some time in the past as the gaskets were not original. The fuel filter was clean as were the bowls. Choke settings were to spec and there was a lot of black staining inside secondary carb throats. I want to use this truck as daily driver, but the drviveability problems and the tangle of vacuum related emissions seem daunting. Also the AIR injection pump is making a lot of noise and sounds like it is about to go.

Any suggestions? We have no emissions checks or compliance in Montana so I am tempted to go with a non-emissions Holley carb and and MSD ignition to see if I can improve the situation. Will these mods kill the value of this original truck? Will a non-emissions setup like this destroy the cats or should they be removed beforehand? Thanks in advance.

the colonel

Welcome to the site I to am fairly new.I have basically the same engine in my 86 also terrible mileage but I only drive it 11 miles a day to and from work.Truck is in the garage right now waiting on a new Holley 4180.I have owned this truck for just over a year and it has never left me on the side of the road.There is a vacuum valve on the drivers side of the exhaust pipe,make sure it is opening once truck has warmed up.I am also waiting on a set of WR4037A wire set to see if that will help mileage.You might want to write that number down in case you ever want to replace them,I had a heck of a time finding the right Motorcraft wire set.
I think the problem with these carbs (4180C) is they are a Calf.carb and the air/fuel mix cannot be adjusted.
What I did with the vacuum hoses was I checked each one and when I was satisfied it was ok I put a piece of masking tape on it so I knew it was checked.
All in all I love my old truck and hope to drive it for another 6 years till I retire.
Good Luck George

GhostriderI

Welcome to the site, I also have the same engine in my 85, cannot tell you the mpg as the fuel gauge does not currently work. But my round trip is about 9 miles . The 4180c carb. has the air/fuel set when built when you put the carb kit in there are instructions on how to remove the tin covers for the fuel/air set screws and adjust them. Found this out when I put my carb kit in. When you put the carb kit in did you check and set the floats and recheck them installed.[instructions are in the carb kit (could be a float out of adjustment and pouring fuel down the throat of the carb causing the engine to run to rich)]

celcius232

I know how to check the float levels with the site plugs and adjust. I did find out the air cleaner duct vacuum motor is out so it is pulling in cold air all the time that may be contributing to the problems. I guess i will have to find another one in the junk yards. I checked the valve on the drivers side exhaust adn it appears free. There could be a vacuum leak somwhere, but I have no idea where to start. I will keep trying and thanks for the help.

GhostriderI

Does your carb have the manual or electric choke? Thinking if electric could have a problem in that circuit. Just a thought.. An yes a vacuum leak can cause problems. I would start at the carb plate and go out, And I like the idea George has using the masking tape to mark each as it passes inspection. I last time I did it I use the post it style sign here label with the arrow. But with the masking tape you can also make yourself notes about the line (from/to, size, or any thing else you may need).
As to the Air pump system you might also want to look at the air supply control valve to ensure function might be blocked causing the pump to over pressure and struggle

Just throwing ideas out. Hope this help or trigger other ideas on where to look.

celcius232

It is an electric choke and I think it is supposed to have 12 volts, not sure if that is continuous voltage when the key is on. The choke sets correctly and it starts easily, but it seems to come off immediately when I touch the pedal. Maybe I need to adjust it for later opening.

I found a TSB that describes replacing the orignal blue choke fast idle cam with a later design. Perhaps that will lengthen the choke operation and hasten the arm up. Has anyone tried that?

The biggest problem it has is the low idle and and rough running until it reaches full operating temp. Then the idle speed increases and it smooths out.

GhostriderI

Cold idle adjustment on the choke could be set to low also.. I think fast idle should be around 1500 to 2000 rpm. Your emissions control label will tell you the rpm for your truck.

chiefdave

I had the same problem on my 85 F150 5.8 HO. The problem was low voltage to the choke. Ran a jumper wire from a key on hot wire and now get 16-19 on hiwy and 14 around town.

celcius232

Hey Chief Dave--the voltage on my choke has now dissappeared and I have no idea why. I was having bad intermittent problems with it until I traced it to the choke not opening at all and it would die (flood) while it was warming up because the choke flapper would not open. Where did you connect the jumper wire and has it caused any problems since bypassing the original choke power circuit? I have not been able to find any freebie engine wiring diagrams for this truck, but someone told me the choke power comes off the alternator.

Scraptor

The power valve can cause all kinds of nasty, and all it takes is an intake backfire to kill one. Then it floods and gags and acts like a stuck float or choke.If it cleans up at high revs but sucks at idle and cruise I'd suspect the powervalve, also the centrifugal advance seizes sometimes and causes problems that act like the carb. Best check that and get a performance recurve kit



Is this the diagram you needed?

V