Classic Z24 symptom?

[Datsinner77]

Hello Ratsun, I have this 81 Datsun pickup 4x4 wich has a z24 out of an 84 2wd automatic pickup. right now I have it mounted behind a 4 speed and was curious if the automatics had differently calibrated carburetors?? my issue that I am having is while maintaining a certain speed under 5 or 10 miles per hour it will run smooth at 1500 RPM but once you take your foot of the gas it will buck and almost die untill you put your foot barely on the clutch pedal. Please any information will be greatly appreciated. I have changed spark plugs to the reccomended NGKs and have rebuilt the carburetor with new bas gaskets as well. possible vaccume leak or distributor?? Thank you Ratsun

[SHORTDOG]

You know i started having this problem and i just ran a couple of bottles of Lucas fuel system cleaner in with better gas and the problem went away....could just be dirty gas.

[Dat Lurka]

I could be wrong but I think there are additional vacuum lines on the carbs designated for auto trans.

[datzenmike]

Take a look at the clutch peddle. There may be a switch there that can be jumpered so the emission system thinks your foot is on it all the time. I think it's part of the fuel shut off on deceleration to reduce hydrocarbon emissions. (it also saves gas too) It turns off the idle cut solenoid at high speed when decelerating. It should turn the idle cut back on long before you get anywhere near idle but this will be easier than trying to find and fix the system. See it this works.

[Datsinner77]

Yeah I was reading in the 1984 service manual and they explain that the clutch switch sends a pulse to the anti diesileing solenoid, but is this just to prevent an anti diesel from occuring or could this be the problem? I know some came with a vaccum switch but mine does not have one..

[datzenmike]

When driving there is fuel available to the idle circuit although not used. At high speeds when you let off the gas to coast the throttle returns to the idle position and this fuel is sucked in when not needed and blows out the tail pipe. A vacuum switch senses this high vacuum and shuts off the idle cut to stop the waste and turns back on at lower speeds. There is a switch on the clutch and a neutral tranny switch to allow idle if these are selected while coasting. This thing actually saves gas.