Digital Throttle Behavior

[Gary in NJ]

Throttle control on my car is difficult at low rpm (off-throttle to on-throttle transitions). It's digital; on or off.

I've lubricated all of the ball joints and linkages at the carbs with white grease to no avail. This weekend I'm going to replace the throttle boot so I figure this is a good opportunity to ensure that the linkage is set-up and adjusted correctly. I've consulted the FSM and have found the following info:

1. Adjust the Tension Rod on the engine side of the firewall between the bell crank and Torsion Shaft to 7-3/16"

2. Adjust the interior Tension Rod between the throttle and bell crank to 4-1/4"

Is there any tribal knowledge beyond this that might be useful to know?

Edited May 29, 2010 by Gary in NJ

[Arne]

The 240Z throttle linkage is rather bad this way even under the best of conditions. Adjusting the rods may help some, but the real answer is to modify the bell-crank to try to eliminate the over-center action of the linkage.

Here's one thread documenting this modification - I searched for "throttle bell crank" to find it.

http://www.classiczcars.com/forums/showthread.php?t=12946&highlight=throttle+bell+crank

[Arne]

Here's a different thread that gives some additional info on this.

http://www.classiczcars.com/forums/showthread.php?t=30584&highlight=throttle+bell+crank

[Gary in NJ]

Interesting reading Arne. Before I go "experimenting" I'll make sure that I'm adjusted correctly. It seems like it would be easier to recalibrate my foot & brain then the bell crank.

I remember the throttle of my first 240Z being sensitive, but not bipolar. It was certainly drivable. This Z is on the verge of undrivable.

I'll report my findings. But if all else fails, I'll try the cut-n-relocate modification.

[Gary in NJ]

Well, I just got in from the garage. I disassembled, cleaned and lubed all of the parts in the throttle linkage. The Tension Rod on the engine side of the firewall between the bell crank and Torsion Shaft was right on spec at 7-3/16". The interior Tension Rod between the throttle and bell crank was long, at 4-7/16 as measured center-to-center of the end caps. I removed the end to install a new throttle boot and reinstalled the end, setting to the FSM spec of 4-1/4".

It all moves very smoothly, but it's dark and driving is different then just pumping the throttle. I'll take it on a coffee-run in the morning.

[Bonzi Lon]

I also have been experiencing this, but only after I changed out carbs, balance tube and linkages. I was able to get a little more slack by bending the rod like I had seen on another Z car years ago. The carb spacers are only 5mm thick because the N36 manifolds have 30mm studs. Other spacers are 15mm and 40mm on the studs.

So far it is working much better than before, like 90% better, still could use some tweeking on the bell crank.

Bonzi Lon

[Bruce Palmer]

The "fix" for this is to go with the thick insulators and the longer studs.

[Arne]

The "fix" for this is to go with the thick insulators and the longer studs.

Is that why my '71 doesn't seem too bad in this respect?

[zKars]

One thing to add about the process of changing the angle between the two arms on the throttle pivot. All threads so far discuss cutting the top arm off then re-welding it at the new angle. That's messy

For the early gen pivot arm type such as Arne's, there is a far simpler technique. Cut right through the tube part about half way up.

Place a drill bit that just fits in the hole to re-assemble the two halves to align them, rotate the top and bottom halves to the new angle (~45 deg verses the original 90ish). Weld and grind until the tube is back to being a seamless tube. The drill bit will keep them aligned so it will slip over the pivot pin on the firewall again. No one will even know you touched it if you do a pretty grinding job.

Try telling the story to someone at a car show that Nissan recognized the problem and issued this very rare part with the smaller angle between the arms and you just happen to have that very rare part. See who you can convince its true!

Jim

[ChrisZ]

How do you want me to do that Jim?

[Gary in NJ]

My cleaning, adjusting and lubing effort payed off. The throttle now moves with much less break-through force. It's now similar to my last Z. So now it's drivable, but after reading the attached threads, I'd like to get a little more improvement.

Bruce, I already have the thick spacers. Will putting the bend in the throttle shaft have any effect?

Bonzi Lon, is that the OEM throttle shaft, or did you have to get a longer unit?

[Mikes Z car]

The PO of my car bent the top arm of the "turnstyle" into a stairstep shape effectively shortening it which slows down the rate of butterfly opeining as the gas pedal is deperessed. I finally noticed my car doesn't have nearly the problem with throttle jerk my old 240Z had as I work on it more than drive it. I also finally noticed that my upper turnstyle arm looks different from other turnstyle arms from pictures others have posted of their upper arm. Other arms are straight, mine is bent. I am putting this on my blog with pictures, don't have access to the pictures right now.

Edited April 4, 2013 by Mikes Z car