Problem installing a Demon 1900 on my 340

[Raycuda]

I have been having an issue installing a Demon 1900 on my 1970 cuda 340 with the 727 Torque flight transmission. After the install I have a throttle pedal bind about 1/4 way of travel. We replaced the throttle cable, but that didn't make any difference. It seems that the carb is sitting too high with the spacer (7/8") that was on the car with the previous Holly carb. The throttle cable is not a straight fit and comes onto the throttle linkage at an angle. Could that be the cause of the binding? Would a smaller spacer solve my problem? Any suggestions would be greatly appreciated.
Thank you.

 

[Katfish]

Can you tweak the linkage bracket to correct the angle?
A pic would help

 

[pschlosser]

Isolate the source of the binding.

Can you feel the binding when operating the throttle lever by hand at the carburetor?

• If so, temporarily disconnect the throttle cable from the throttle stud and test again.
  • If the binding is no longer present, you know its the cable, and perhaps the angle it attaches at the clamp.
  • If the binding is STILL present, look at the throttle pressure linkage
• If not, disconnect the throttle pressure linkage, and test again at the pedal. If the binding is still present, when operating only the throttle lever, it is either the cable or the carburetor.
  • Next, disconnect the throttle cable from the throttle stud, and using a helper to apply a slight and consistent drag to the throttle cable in the engine compartment, test again at the pedal.
    • If the binding is still present, then it's definitely the throttle cable, and/or the angle of the cable at the clamp.
    • If no binding present, it looks like its the throttle shaft lever, and/or binding within the carb. Check the clearance of butterflies to throat opening at the intake manifold.

If after all the testing, you still cannot find it, remove that wild 7/8-inch spacer and test again.

And like Katfish says, a couple images of the throttle bracket and cable clamp would be nice. A low picture from the front, showing the angle of the throttle bracket as it comes off the intake manifold bolts would be really good, too.

 

[Ricks72Chlgr440]

Would be so much easier for you to go with a Lokar throttle & kickdown kit. I too fought this until I went to the Lokar setup and never looked back.

 

[MoparCarGuy]

@Raycuda
The factory 340 cast iron intake manifold is a square-bore and used a a Carter AVS square-bore carburetor. The primary bores in the intake manifold are 1.44" (just over 1-3/8") and the secondary bores were 1.69" (just over 1-5/8"). The Holley Street Demon 1900 is essentially a three-barrel having two primary throttle blades and one large "goggle" secondary throttle blade. The Street Demon primaries are 1.375" (1-3/8") which will clear the intake manifold primary openings but the secondary "goggle" valve diameter (see photo below) is 1.747" (essentially 1-3/4"). This larger secondary diameter will not clear the factory intake manifold opening of 1.69" if the carburetor is mounted directly to the intake manifold.
Holley's Street Demon comes with two thin gaskets and a thin steel sealing plate which are required to isolate the idle-air circuits by covering air/blow slots on the base (red oval and rectangle below) and reduce heat transfer from the manifold. Holley Video on Street Demon features

A thicker carb base gasket (5/16") or a thin open plenum spacer (1/2") may raise the carb enough to allow the throttle plates to clear the intake manifold bores AND allow the electric choke housing to clear the intake manifold's factory exhaust-heated chokewell. The electric choke on the Street Demon might clear the 1970 manifold's chokewell but check it to make sure. Either way you will need additional gasket or spacer height for the Street Demon secondary throttle plate to clear your factory 1970 square-bore intake manifold.
That interference being remedied, your throttle should regain its full travel from idle to fully open.

The next issue is the throttle cable and throttle pressure linkage alignment to the now raised Street Demon. The easiest but somewhat pricey fix is to go to the full Lokar cable system for both the throttle and the throttle pressure linkage. This setup moves the attachment points up and directly inline with the carb's throttle linkage without the use of a separate throttle lever adapter attached to the Street Demon.
The full setup can run about $250 plus to purchase and will require a bit of installation labor to get it cut-to-length and set up right.

Otherwise, you will need to use a throttle lever adapter to attach your factory throttle stud for your factory accelerator cable (now misaligned) and your throttle pressure linkage (also somewhat misaligned). Your factory throttle cable bracket is not tall enough to get the geometry in line so you may need to bend/extend/tweak the bracket (angled upward) to correct the misalignment. The factory cable is finicky at the junction of the cable sleeve to cable holddown barrel (see red oval in photo below). Good alignment is necessary for full-throttle actuation and proper operation of the throttle pressure linkage.