A few months back I bought a '68 F250. I've been using it as
my daily driver while the Ranger is laid up and it's been a fun old truck, but
there were a few problems with it, some due to its having sat for ten years
before I bought it.
When I bought it, it
had a stock Motorcraft 2-bbl carb on it, and it
turned out to be the wrong one for the truck. It was jetted too lean and
wouldn't run decent unless I had the choke part way out. I then hit the local
wrecking yard and scrounged up a practically new Holley 4412, a 500 CFM 2-bbl
which I bolted on and found an immediate improvement.
But not being one to
leave anything alone for long, I soon began to want more and had visions of a
4-bbl lurking under the hood. Now there just happens to be one, a
brand-spanking new Edelbrock #1405 600 CFM mechanical choke 4-bbl. And this is
the story of what I had to do to make that happen…
"How hard can it be
to swap on a new carb," you may ask, "and why would I need to read an article
about doing it? I can just bolt the thing on and go, right?"
Well, there's a bit more to it than that and I want to lay
it all out for you here. Now, I probably would have been content to do a simple
carb swap and leave it at that, but since I had a stock cast iron 2-bbl
manifold, I thought I'd take the opportunity to swap that out for a 4-bbl
manifold and do some under hood clean up and detailing at the same time. But
that's another story.
So let's assume that you already have a 4-bbl manifold in
place and the next step is to install your new Edelbrock carb. First you have
to choose the right one for your application. My truck came with a manual choke
stock so I wanted to stay with that and the 360 FE is also bone stock, so a 600
CFM should be just about right for it.
The Edelbrock carb
comes neatly packaged in the box you see here, along with sufficiently detailed
instructions for even the novice installer to comprehend. There's also a nice
little owner's manual that details the inner workings of the carb and what you
can do to custom tune it if necessary, but it'll often work great straight out
of the box.
It also comes with a new base gasket, air horn gasket and piece of 1/4" all-thread
for an air filter stud, and a little bag containing various goodies such as
vacuum caps and a tee, a 1/4" plug for the brake booster port, and a linkage
There's no substitute for planning ahead, so inspect
everything carefully and try to determine what additional parts you're going to
need in order to complete the installation, so you can get everything ahead of
time and save on trips to the parts store. (Unless you happen to live next door
to one...wouldn't that be cool!)
Before getting started with pulling your old carb, you need
to determine if your distributor vacuum advance works off of manifold vacuum or
ported (also known as timed) vacuum. With the engine idling, pull the advance
hose off of the carb fitting and hold a finger over the fitting. If there is
vacuum present then you have manifold, or full vacuum
to the distributor. If there's no vacuum however, then you have ported or timed
vacuum, which comes into play as engine speed increases. With this determined,
go ahead and yank the carb.
installed the pipe plug in the brake booster port at the back of the new carb
since my brake booster has its vacuum source on the manifold. Be sure to use
thread sealant here.
Next I installed new studs on the manifold using shorter
ones than the originals, since I would no longer be using the heated manifold
spacer. I would be using a 1/4" insulated spacer, and took that into
consideration in determining my stud length. Edelbrock recommends using the supplied
open gasket only with an open-plenum, single-plane manifold so I used a 4-hole
spacer. Be sure to check it for fit against the carb to make sure the holes are
the same size as the carb ports and that the secondaries will open.
Next I set the carb in place to check for clearance and
throttle arm would need to be lengthened so I dug into my stock of parts for a
longer one. You can see the difference between the two arms in the pic below;
the longer replacement arm is installed on the carb while the old shorter one
is laying on the manifold below it:
Then I moved on to the choke cable. The old one was held on
to the carb choke linkage by a setscrew, but the Edelbrock carb has just a
small hole in the linkage, which necessitates a double bend. Not hard to do,
but if you have a small engine shop nearby they should have special pliers
which crimp that little double bend into place, they may be willing to do it
for you if you feel like taking the choke cable out of the truck and taking it
in to them. I didn't, so I just bent it myself. Not as clean or as tight as the
special pliers will do, but serviceable.
Then, simply thread the cable end into the linkage and
secure the housing in the clamp, making sure to check the throw of the choke
knob for proper action and adjustment.
everything properly fitted, go ahead and bolt the carb down. Tighten the bolts
evenly, corner to corner diagonally but don't over tighten. Edelbrock won't
warranty a broken carb mounting ear!
Edelbrock also specifies that a new filter must be installed
or the warranty on the carb will be void. Mine was replaced soon after I got
the truck running, but I knew it'd had some bad gas run through it since then
so I bought another filter. My old 360 has the cartridge-type filter in a
canister on the fuel pump which has a lot of filtration surface area, so I
didn't feel the need to add a second in-line filter. Edelbrock also recommends installing new
spark plugs at this time.
Another consideration came in the way of the fuel supply
fitting on the carb. The supplied fitting takes a 3/8” hose (although a 5/16”
can be stretched to fit), which comes straight into the passenger side of the
carb at the rear.
stock fitting must be cut off the end of the fuel line and since there is no
flare to help hold the hose in place, I used two clamps. I like the little
spring clamps, they have good holding power and are impossible to over tighten.
I also used new hose here.
If you stay with the stock air cleaner it should clear just
fine, but if you go to a low-profile type air cleaner then you may find you
have an interference problem. I did, so I got this nifty little adapter with a
banjo fitting to reroute my fuel line, and it has the added benefit of giving a
cleaner look to the installation.
From this point on there are just the little details, such
as routing of hoses, etc. You can see I used a nipple to connect two different
hoses together so I could use the formed PCV hose I already had, and then I
hooked up the vacuum advance hose to the timed vacuum port on the front of the
carb (the one that has the cap on it in the picture). I also took this
opportunity to replace the PCV valve, getting rid of the rusted antique that
used to reside in the breather.
Once you've double-checked all your connections, crank the
engine to fill up the float bowl and check for leaks at the lines and connectors.
Once you've got fuel, it should fire up. Let it warm, and adjust the idle speed
if needed. Once it's warmed up, adjust the mixture screws as per Edelbrock's
instructions, install the air cleaner and you're ready for the test drive!
Right off the bat I could feel the difference. The throttle
response was excellent and I could detect no flat spots. It definitely has more
power; in fact it's a challenge not to break the rear tires loose on hard
acceleration. And of course there's the sound of the secondaries opening, that
good ol' 4bbl roar.
I'll have to give it a little time and get a few tanks of
gas through it while I check my mileage, and of course that won't be great till
the novelty wears off and I start to drive sanely again! And of course I'll
need to read the plugs, but it feels like it's pretty close right out of the
box, just as I'd been told to expect with this carb. Overall, I have to say I'm
Hopefully, you will be too!