A common problem on inline
engines that have carburetion upgrades is throttle
linkage. Most modern carbs are designed to operate by
cable throttle, not the primitive rods found on most
early engines. The following deals with GM inline
sixes but same principles apply. It can also apply to
multiple carb installations where two or more carbs
are linked together and operated by a single cable.
There are certainly many ways to skin a cat, but here
is a solution I used after trying several others.
The diagram above shows how a
4-barrel carb should be mounted on an Inline engine.
Note that the secondary throttle bores are inboard and
parallel with the cylinder alignment. Now, there may
be some carbs where this just can’t work, but it is
appropriate for most modern (Holley, Edelbrock, etc)
4-barrels. If you mount the carb sideways like a V8
it’s easy to see that fuel distribution is going to
be unequal. The engine will run - but you will lay
awake at night, just knowing that one end of your
motor is getting more than its share of fuel!
Unfortunately, as these carbs
are designed for V8 applications, when we mount them
on our inlines the geometry for linkage is now all
wrong. Rather than a simple "north –
south" push / pull action, the cable now has to
operate "east – west". If you look at the
photos below, you will see how to overcome this
problem. The bellcrank on the side of the block is a
Mr. Gasket product and carries a part number of 1523.
There may be others, or you can make your own. This
bellcrank is completely adjustable and sells for about
$15. It will require that you turn down the bellcrank
stud on the side of the block because it is a smaller
diameter than the factory bellcrank. This bellcrank
allows you to use the original accelerator pedal (or
"Foot Feed" as they used to be called). Just
hook the original rod to the lower arm of the
bellcrank, as it was on the original. You may be
tempted to use a fancy billet "spoon" type
gas pedal, but this can lead to problems. On my ’51
GMC truck there was just no way to mount this type of
pedal and still have a comfortable driving position.
Maybe on a T-bucket or some other kind of roadster it
would be OK, but in an old truck, it just makes for a
very uncomfortable foot angle.
The photos are mostly
self-explanatory but here is a little bit of
additional info. By use of the bellcrank you convert
the "push" motion of the accelerator rod
into a pull motion. So, you attach your cable to the
top "pulling" arm of the bellcrank. The
cable I used was from Lokar Performance and it is a
nice braided stainless piece. A motorcycle cable could
probably be used here too, with a little ingenuity.
You will have to make a bracket to hold the bellcrank
end of the cable sheath. My bracket is painted the
same color as the engine so it doesn’t show up too
well in the photo, but you can do yours in any
convenient place on the side of the engine depending
on location of headers, alternator etc. Just be sure
that the bellcrank exerts a fairly straight pull on
the cable. If it rubs the sheath, it will fray and
eventually break. Then you just loop the cable around
and hook the other end up to your carb. I found that a
linkage bracket from a V8 worked fine, with a little
grinding to provide clearance to the intake manifold.
Be sure to avoid tight bends
in the cable. In the lower photo, note
the gentle bend of the cable (just under the oil
lines). Final adjustment is done with the cable ends.
I did not use any additional spring beyond the carb
return springs. This setup has worked faultlessly for
several years and many thousands of miles.