Carb Linkage

[240Z240Z240Z]

I've had a problem with my car for a long time and am wondering if this is typical of the car, or unique to mine.

When I press on the go pedal there's considerable resistance then it breaks loose and the car lurches forward. It's hard to make a smooth take off. I checked the linkage and everthing is smooth and free turning with the engine off, then I started the car and the stiffness is there. It's like the vacuum on the throttle plates is causing the resistance. Does anyone know about this problem and how to correct , or minimize it ?

Thanks for any help.

[240ZX]

Doug,

This is a common issue on the old Zs. Some of the problem is worn parts and the bigger problem is in the adjustment of the throttle linkage. You are dealing with bell crank geometry issues! Basically, the farther a lever arm move off the 0 degree position (mid point of travel arch or when the lever arm is 90 degrees to the driven link), move force is required to move the lever arm. So what is happening is, that when you first apply pressure to the GO pedal the lever arm is way off the 0 degree position (requiring more pressure to move the pedal) and as the pedal is moving down the lever arm gets closer to the 0 degree position (it gets easier to push the pedal). Mind you, when you get to full throttle the same event occurs ( more pressure is required to move the pedal) but you will not really notice it as much. So, its a matter of looking at the position of the bell cranks on the throttle linkage and adjust them to minimize this effect. Any play in the linkage will not help the matter either. In my case, I had excessive play in the bushing that the rotating linkage (shaft running from the firewall to the carbs) rides in next to the firewall. When I fixed that the throttle was more positve. There are some old write-ups on this subject that provide a better description than I have provided. Wish I could remember which site it was on. Hope this helps some and good luck.

[240Z240Z240Z]

The resistance only occurs when the engine is running, so the linkage must be laid out in such a way (lever arm) that the a small amount of resistance at the throttle plates equals a lot of force at the pedal. I'll take a closer.

Thanks for the response.

[240ZX]

Doug,

Another thing to check as well is the condition of your engine mounts. The drivers side (USA models) engine mount is more susceptible to failure, due to engine torque pulling it apart. If it has failed and allows the engine to rock to the right under acceleration.....it will add to your problem. Just something else to check!