mechanical throttle linkage, what's the problem ?

[Captain Obvious]

Check out the venturis on that beauty!! :kiss:

[240Z240Z240Z]

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.

[SledZ]

Here is what I did and it is as smooth as can be.

http://www.classiczcars.com/forums/tech-pubs-howto/12946-sticky-agressive-throttle-fix.html#post85160

[Kennymonster]

In my opinion this whole jerky acceleration issue is very subjective on the driver & feel.

My '72 started out on bone stock SU / linkages, I never once felt the needed to increase the linkage angle or desensitize the throttle sensitivity. I personally didn't think it was that touchy compared to other cars I've been in, but then again it all depends on preference too. I don't feel right telling someone to get used to it if they don't like the feel, it's your car after all.

I converted to triples and kept the 100% linkage set up on that too, from pedal to the carbs... until one day a socket arm came off on the freeway leaving all other linkages completely useless, all it takes is one.

The Lockar kit in post above, I had it laying around and decided to rig it with my interpretation of it. I wanted ALL the linkages gone (minus the signature 3 arms on the carbs).

Removed:

Drilled out the pedal to mount the hook side, backwards from what other write ups said:

Completely eye balled this boat bracket on ebay, the mounting holes lined up perfectly on my mikuni carbs. Bent it slightly to my desired angle, and drilled out the top portion to sandwich between the kit lock nuts.

The threaded end of the Lockar kit, I found a plastic socket with the right pitch so it can thread on to it, effectively making it very simple and direct without having to fab any custom brackets and shenanigans. The slight curvature embracing my fuel line was a bonus.

And the end result, is very short and responsive, yet controlled throttle on my triples. My foot may as well be on the carb arms themselves. The difference in response is very apparent on throttle blips on down shifts / heel toe, and take offs as well.

[Captain_Zeros]

I'm running SUs with the bone stock linkage and I've never experienced any sort of jerk or difficulty in modulating throttle at all.

Now I'm real curious what everybody is talking about. :tapemouth

[SledZ]

Have you ever play that game Shoot the Moon? It's almost like that. You put pressure on the pedal and it's hard to get it to move and then all of a sudden it lets go.

[Zedyone_kenobi]

This is 100% a worn throttle linkage thing. I would bet the house on it. After I replaced the linkage (with new Ztherapy SU's) my car drove exactly like any new OEM car on the market, engine running or not. I had the smoothest pedal I ever had. NO sticking ever. It may not be about lube as much as it is about suble angles and worn ball and sockets. The first thing I would do to a new to me Z car is replace all those linkages with new ones or at least new ball ends.

[bartsscooterservice]

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.

yeah when engine is running, it feels like engine vacuum is pulling on it

my dad had one in the 70's and he said didn't have it, so must be a wear problem. Still thinking the carburetor axle and the linkage on the manifold cause to much resistance due wear.. but didn't have time to check it yet, will do saturday

[240260280z]

I wonder if the edges of the throttle valve are the culprits and they embed a little into the aluminum wall under vacuum due to wear? Can vacuum do more than this?

[SledZ]

I would believe it was wear if after I did the "old throttle fix" and the symptom stayed the same.

[Mikes Z car]

Blue,

I was wondering if dirt in the four butterfly shaft bearings as they go through both sides of both carbs would cause friction that would cause the jerk? Maybe spraying the bearings with carb cleaner would help? I haven't seen a clear picture of what the butterfly bumps into at its top and bottom when it is closed. Maybe wear on the shaft bearings would let the butterfly contact the carb wall in a way it didn't when it was new?

[bartsscooterservice]

yeah something like that, I checked between work today but couldn't find anything odd. But if the butterfly valve was contacting the throttle body, then wouldn't it also be when the engine is not running ? It's only when it's running...