sticking throttle issue

[Voyager]

Need help diagnosing an occasional sticking throttle issue. Have SPO 2920 with a KC 408. At rest, the mechanical linkage articulates smoothly from the gas pedal to the carb (see pic). However, while driving, the throttle occasionally sticks (rpm fails to drop between shifts and/or idle rises enough to cause unwanted acceleration). Tapping on the gas pedal drops the idle back down. Only happens occasionally. Inside of carb looks clean. Thoughts?

[Jerry Clayton]

Floor mat?????????????????

[Voyager]

One of the first things I did was remove the floor mat. Can stick my foot under pedal and nudge it back to pull rpms back down. Was thinking about running some carb cleaner through the carb.

[chucks1]

Weak or impaired return spring on the throttle pedal under the dash?

[Cobra20646]

OR no return springs. Should have dual springs at carb for safety.

taking another look at your photo, it looks like the spring(s) are laying on the intake manifold???

[CHANMADD]

If a loose engine mount the engine may shift.......Some older carbs get some wear on the throttle spindles
and the shaft can get slightly cocked and stick...........my secondaries have a slight stick
so I put and extra.... ..third ....spring on the secondary shaft......

[Voyager]

OEM spring is in place (see pic). Also added a second return spring to the carb (as seen, but not attached on first pic). Maybe I’ll try a stiffer pedal spring.

Carb springs are temporarily off to feel for friction points as I manipulate the linkage through it’s range of motion.

[Jerry Clayton]

Change the linkage set up so the arms on the cross shaft on the fire wall point upwards instead of down-----and use the double carb return spring setup out there(one inside the other) to pull forward on the carb arm---it is best to have throttle return springs right at the carb primary shaft instead of the peddel---

[Voyager]

Chanmadd,

You may be on to something. I’ve noticed that the linkage rods (throttle spindles and the shafts?) have a slight stick when rotating them clockwise or counterclockwise.

I adjusted them when I change out the engine mounts a couple years ago. Also adjusted them again last summer to move the gas pedal to help with heal & toe.

Can’t fell any sticking when opening and closing the throttle linkage, but can feel it when spinning the rods.

Bob

[Voyager]

Jerry,

Regarding setting it up so the arms on the cross shaft on the fire wall point upwards instead of down – are you talking about the shaft under the clutch reservoir? I will try that.

Regarding the double spring setup to pull forward on the carb arm – are you saying attach the double spring on the front side of engine and have no spring attached to the other side?

Bob

[Jerry Clayton]

yes--hook the springs to the same point that the linkage hooks to the carb arm---It will be pulling at the primary point for return--there will be nothing lost in any linkage bind such as with the spring at the pedal---also with the arms on the cross shaft on the firewall pointed up you will have everything orientated the same way(no change of direction)

And , have the springs set up to pull the throttle arm tangent to the mid point of travel(most effiecent geomentry)

[CHANMADD]

Like Jerry said....you absolutely have to have springs at the Carb.....and also try the links like he said...

[Blas]

A mentioned, a return spring (double springs actually) are a must, but I would also investigate the motor mounts. If the engine is twisting under acceleration due to a damaged or loose motor mount, no spring will compensate for that. Might also check the rear mount on the transmission if the motor mounts are ok.
The return springs in the footwell are not what returns the pedals to neutral positions, they actually prevent the pedals from rattling around when not engaged or their movement arrested with your foot.

[Mark Brye]

If its just hanging up a little, and you don't feel like its in the pedal, could it be an issue with the mechanical advance in the distributor? I had an idle issue for a while and it was the advance "arms" (for lack of a better term) had started to get gummed up from distributor cap/rotor dust.

[Rick Parker]

Voyager: The arms should be oriented so they travel parallel through their motion ans as previously mentioned orient the arms to be pointing up.
Back the idle speed adjustment screw all the way out so the throttles are closed, then adjust all the arms so you have full motion. Attach the spring(s) to the carb at the same place as the link from the pedal arm, but pull the carb lever to the FRONT(from the top), it will have less wear on the throttle shafts. After doing this, then adjust your idle speed screw. By doing the above FIRST you will have created a very small amount of "Free Play" in the throttle pedal to allow for heat expansion and engine movement. One last thing, be sure the carb is evenly tightened on the 4 corners and a good gasket is being used. Uneven torque can cause binding of the throttle shafts after the engine warms up and things expand and move a little, and of course lube all friction points and throttle shafts lightly.

Once you are satisfied with the above consider Mark's topic; it is a good one regarding the mechanical advance potentially sticking or if the springs being used in the distributor allow it to "Hunt" and thus allow small changes in the timing at idle.

Report back

[Voyager]

Thanks for all the feedback. I’ll work through the recommendations and report back.

Bob

[leaseline1]

Ok, I see you have a choke on the carb but cant tell if its a pull choke or electric choke from the picture. If its electrical, I recently had a virtually identical issue appear after servicing my carb and it ended up being a little detent between the electric choke mechanism and the main body hanging up near idle. Also was causing some richness as the choke was slightly hanging closed. If its a manual choke, then still check the choke to be sure it works freely. Personally, I cant stand Holley chokes with performance cars. Curious what the outcome is and good luck!

[Voyager]

Update.

Per feedback, rotated cross shaft arms up and re-adjusted all linkage connection points. Added new return spring mount forward of carb arm and installed new double spring. Double checked that engine and tranny mounts were good (they were). Test drive revealed no sticking throttle.

Interestingly, the application of power seemed to come on a tad softer (maybe less violent is a better word). Maybe the new throttle linkage position now allows the pedal to move further in relation to the movement of the carb arm. Who cares? All is well. Thanks all.
Bob

[Jerry Clayton]

Interestingly???????????????? Yep---many dirt track racers have to change throttle linkages to slow throttle opening-------------

[Voyager]

Resurrecting my 2 year old thread. The throttle still occasionally sticks. Seems to happen only after I shut the hot engine off for a short period of time. Almost as if fuel coagulates in the hot carb. After driving for 10-15min, the sticking stops....like the gunk was dissolved by the fresh gas.

Thoughts?