Throttle Linkage for Inlines

~Jack Halton~


    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.

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    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.

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    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.

- SafeSix