Gas pedal question.

[Tom Selleck]

I have a 1972 240Z, and the gas pedal seems to be too responsive. When you put it in gear and press the gas slightly, it's fine but when you let out the clutch and give it a little bit more gas, it revs to around 3k RPM and above, and that leads to hard takeoffs which aren't the best in city traffic. There is no middle section between giving it a little gas or a lot of gas.

Are all Z's like this, or is it just a spring or something that needs replaced? Any help is appreciated, and if I was unclear about anything just let me know. Thanks.

[2ManyZs]

If you look between the carbs, you should find 2 springs that are attached to the linkage and down to a small hook on the carb heat shield. If there aren't 2, you might want to find a pair the right length at the local hardware store.

Also, it never hurts to pull the plastic ball sockets on the linkage apart and clean and lube them with some light grease. Also, pull the E clip off the top of the linkage bellcrank on the firewall and clean and lube that also.

Sounds like it could be a combination of too light a spring and/or linkage that needs to be cleaned and lubed.

[Z Babe]

I absolutely agree with Keith. I had to replace the throttle spring on my 82 ZX a few years ago. When I sat at a traffic light, my engine would rev to the point of redlining. I managed to make it stop by putting my foot underneath the gas pedal and pulling it up -- had to do this while I was waiting for the spring that I ordered to be shipped to the dealer.

[EScanlon]

There was a discussion regarding the geometrics of the bell crank that is used to transfer the front to back movement of the accelerator pedal to a side to side movement in order to actuate the carburators.

It seems that since you are dealing with rotational movement, at 90° of offset, (in the "corners" of the circle) you are at the peak of the curve for maximum movement per radian of angle. However, this is also a situation where it takes MORE force to begin the rotation than it does to maintain the rotation once you have exceeded the point of inertia release. The resulting OVER acceleration, or in different terms, the tendency of your foot to "push down harder" than you intended, is what is giving you what appears to be a jolt through the clutch.

Unfortunately to correct this pre-loading / release of the bell crank would require changing its angle of action. Various items have been proposed, and if I recall an offset of something like 12° (i.e. reduce/ increase offset of arms) yields the next best situation, which is where the initial force required to actuate the pedal is equal to the force to continue the thrust.

I hope I explained it well, please correct me if I erred.

Enrique

[240ZX]

Tom,

The situation with the early Z throttle linkage can be improved. You should first do what 2manyZ's suggests. However, one of the real problems is 30 some years of wear that has taken it's toll. If you can get rid of as much play as you can in the linkage, use the adjustable links to position the bell crank properly, and slightly reduce the return springs tension you will end up with a throttle that feels and responds almost linear. I had the same problem you are talking about before I started my redo on my Z. Some time ago I found a post, written about 1970 something, by this engineer guy who went into great detail about this problem. Basically he said it had to do with the position of the bell crank, because when a bell crank is actuated by the driving rod (the one that comes through the firewall) the result of the driven rod (the one that parallels the firewall) the resultant travel of the driven rod is not linear to the driving rod....hence the strange throttle pedal feel. I actually had to read the post a number of times before I understood what he was talking about. Anyway, I found that most of the play in my linkage was from the very worn bushing that the rotating part of the linkage rides in and the end of the rotating rod that sits in the bushing. I couldn't figure out how to replace the bushing so I fabricated a new end for the rotating rod that was big enough to get rid of the play. I little bit of work to make it happen, but the end result was worth it. I did replace the stock return springs with stainless steel springs that have slightly less tension. Now my throttle works like you would hope a throttle would work.....smooth and linear. So, to some it up....get rid of the play in the linkage, lube it, and adjust the bell crank position.

P.S. At one point I even considered installing a more modern throttle cable assembly, but as you might guess that involved even more fabrication of parts.

[2ManyZs]

There's a thread somewhere around here that had a pic of how to bend the one rod to improve the throttle feel, but I'll be darned if I can find it now....:stupid: I'm fairly sure Daniel posted the pic... but my memory is getting worse by the day too.....:cross-eye

[Tom Selleck]

Thanks for the help, everyone. My dad and I greased up the plastic ball sockets a while back, and that didn't help. I did a search on the forums, and found other solutions to try. Thanks again!

[Victor Laury]

Tom,

I'm following your plight with interest. My linkages, springs, etal are in new or perfect condition. But something is wrong with the geometry for sure! I can get into a surge cycle that tries to snap my neck.

[Jimbeaux]

There's an article regarding this on www.zhome.com under Technical Articles called "Improving your throttle Linkage"

Hope it helps.

[Victor Laury]

Thanks! Found it. Here's a link straight to it

Getting Rid of The Jerk

[2ManyZs]

Hmm, isn't that a coincidence... the guy that wrote that lives in the same town I was born and grew up in....wonder if he still lives there...and I just spent a week there the end of June, no more than a mile from his address......

I'm hearing the theme song from "The Twilight Zone" in my head now....