mechanical throttle linkage, what's the problem ?

[bartsscooterservice]

It's understood that the mechanical linkage isn't ideal, but I can't believe they would have sold the cars new with the linkage as jerk inducing as I've experienced or a lot of people wouldn't have bought them after a test drive. Do any of the early Road and Tracks or other publications talk about the jerky throttle problem ? Not sure, but I don't recall having ever read about it. I don't think that worn linkage is the problem, like most people I've over lubed every friction point in the linkage path and still no joy.

I've noticed that the accelerator pedal resistance problem occurs only when the engine is running, if the engine is off the throttles open easily. With the engine running it takes more force to crack the throttles open than it does to rotate them from there on, even when you use your hand to move the linkage at the carbs. I think this is just a function of the throttle plate design in that the manifold vacuum is trying to hold the plates closed at idle, so it stands to reason if you reduce your idle speed the problem should be reduced since less vacuum is being created and therefore it will take less force to overcome it. I currently have my carbs off for a servicing so I can't try it myself yet, but I think idling your engine down should have a positive effect.

If you found a solution let me know ! My dad also said something about idle speed, but setting it back to 800 rpm didn't have any effect

[bartsscooterservice]

took the gas pedal off, and cleaned/lubed the rotating part, it helped again in anything above 1500 rpm , but still not the heavy part in the beginning for driving away

[240260280z]

you could try wiring just one return spring for an experiment

[240Z240Z240Z]

If you found a solution let me know ! My dad also said something about idle speed, but setting it back to 800 rpm didn't have any effect

I was thinking lower than that, more in the 500 - 600 rpm range. Not sure what the manual says is correct but I don't think there's any harm from idling "too" low.

[bartsscooterservice]

That's really to low imo , I've set it just under 1000 rpm, like most cars do here. But I tried with the linkage unhooked, and feel how the butterfly valves operate on a running engine when turned by hand, and they still operate heavy, so.. problems with worn shafts then ? I can't seem to think of anything else at the moment. There's no play in the linkage.

Could a to heavy damper oil, or a shortage of incoming air cause this to ? Altough I can't see a direct connection

[bartsscooterservice]

I asked a professional carb rebuilding company from Belgium ( not so many around here ), and he says he doesn't understand why the gas pedal operates smooth when engine is off ( only on the pedal, because direct @ carbs you can feel the tensions of the springs ), but heavy when engine is running.

[Captain Obvious]

I've got something similar with my FI throttle body:

http://www.classiczcars.com/forums/fuel-injection-s30/48078-sticky-throttle-body-hanging-idle.html

I think I have traced the issue to wear in the throttle plate shaft. The shaft is chrome plated for wear resistance and the plating is worn through in spots. The softer gummier steel underneath gets sticky against the soft steel bearing inserts that are pressed into the throttle body casting.

I've "temporarily" fixed it by increasing the return spring force. Addresses the symptom, but not the cause. Eventually I plan to come up with a better solution that addresses the cause instead of just the symptom.

[240260280z]

It is interesting it is on TB's and Carbs. Bearings/Bushings, linkage and TV are common to both so no elimination due to EFI change.

btw my 2004 Rav4 has electronic throttle and it is jerky and insensitive at low speed... I think it is the programmed curve or lack of fine digital granularity at low pedal travel region.

[bartsscooterservice]

I bounced up a topic in the carb section, that guy has exactly the same problem i'm having, curious if or how he fixed it..

[Captain Obvious]

it is jerky and insensitive

Same thing has been said about me at times.

[240Z240Z240Z]

I asked a professional carb rebuilding company from Belgium ( not so many around here ), and he says he doesn't understand why the gas pedal operates smooth when engine is off ( only on the pedal, because direct @ carbs you can feel the tensions of the springs ), but heavy when engine is running.

I still believe the problem is that the manifold vacuum is helping hold the butterflies closed at idle, its just the nature of the design. The carbs have a mechanical advantage over your foot so it doesn't take much resistance on their part to increase the effort it takes to press down on the pedal. What makes it worse is the force of your foot and the resistance of the butterflies causes the linkage to bind in-between, especially at any dry rotating linkage points. You should be able to test this with the engine off by having someone hold the butterflies close right at the carbs and see if the pedal doesn't get a lot harder to press down.

My 2 yen.

[Zedyone_kenobi]

If that is the case, then this problem would be apparent on brand new Z cars with brand new carbs. Which it is not and was not. I still hold that this is a worn part problem, either in the ball and sockets or in the carb bushings