Just tuned both of my recently remanufactured SU Carbs and filled them up with ATM fluid. THe car drives great at high speed, however in 1st and 2nd gear when releasing the clutch pedal and accelerating slow, not hard! Imagine getting in a traffic jam or passing a Street bump, the car presents a shaking back and forth motion. Could this be a distributor problem?? Bad Timing or  Could the distributor need some inner cleaning with WD-40 or Contact Cleaner?? I have a recently installed Pertronix Ingitor and coil which is delivering the correct spark!!

Could be motor mounts open hood and do a take off and see if motor lifts up.

That's a good guess. That would change the throttle linkage position as the motor rocks.

Clutch chatter? Does only occur while pulling away from a stop?

Just increased the timing to 12 BTDC, hesitation is still present at 1st gear and when decelerating and shifting to 2nd gear at low rpms. I read in another fórum that it could be a float level issue! Both of these carbs were fully remanufactured by Ztherapy! Will i need to open the float valve compartment to adjust the level? It sounds as they had it set up perfectly before shipping them to me!

Hesitation or shaking? You're saying two different things. I 2nd clutch chatter due to worn or separated motor mounts based on your first description of clutch release at an idle or low throttle. That sounds to be clutch chatter, and if you have a segmented clutch like a 4 or 6 puck, it'll be greatly pronounced.

If it doesn't have anything to do with the clutch and you are talking about a choppy idle and what feels like a misfire, idle the engine and pull each plug wire off a plug one at a time replacing it after you pull it. You may notice a drop in rpm for every plug you pull. If not, pull the plugs that seemed to provide the least decrease in rpm and look at them. Compare them to other plugs. I'm guessing you're rich and fouling while idling.

Since you're playing with timing, I'd put it back for now, but confirm your mechanical/vacuum advance is working and not stuck.

After playing with your carbs, did you hook the vacuum advance back up?

Did the car do this before you played with your carbs?

If Ztherapy did your carbs, you can take it to the bank that it ain't the float levels.

Let me see if i can explain this better. Just got a confirmation from Ztherapy of not touching the float valves as they are set perfectly.

 

First i get the car warmed up for 5 minutes. Start going in reverse to take it out of the parkway. Slide to gear N° 1 with the clutch stepped, reléase the clutch and start accelerating normally. The car starts to shake back and forth. To avoid this you need to step on the gas fully for it to pickup. Another scenario where this is shown is the following:

 

Passing through a slightly broken road at 1st gear or after a Street bump. THe car has a recently installed Carter P60504 Fuel pump:

 

http://www.ebay.com/itm/Carter-P60504-Universal-Electric-Fuel-Pump-/371170716452?fits=Make%3ANissan%7CModel%3A240Z&hash=item566b7fab24&vxp=mtr

 

which is measuring 3psi. So i dont think its a fuel starvation problem.

I too think it's possibly in your drivetrain, FWIW.  

 

Maybe take it to a transmission shop and have someone drive it?

  On 6/1/2015 at 4:36 PM, jalexquijano said:

... Start going in reverse to take it out of the parkway. Slide to gear N° 1 with the clutch stepped, reléase the clutch and start accelerating normally. The car starts to shake back and forth. To avoid this you need to step on the gas fully for it to pickup. Another scenario where this is shown is the following:

 

Passing through a slightly broken road at 1st gear or after a Street bump...

This sounds like the typical drivability issue due to the as designed throttle linkage geometry of all 240z's. Here is a good discussion on the subject:

http://www.classiczcars.com/topic/47250-mechanical-throttle-linkage-whats-the-problem/

Sounds like a big vacuum leak or a fouled plug. If there was a vac leak big enough to cause that, you would be able to hear it by listening to the engine while the car is idling, unless it's a bad or clogged PCV valve.  Maybe you checked that already.

 

Cars don't lug (run under load in at too low rpm) very well with a fouled plug. If you slow down for a bump without downshifting the rpm drops, and if you have a fouled plug it would shake. When you bring the revs up it runs better. This happened to me recently. I cleaned the plugs (and leaned the rear carb) and that fixed it instantly. Plugs can foul fast, in a day or two.

 

Fortunately we have old cars so it's very easy to check and clean the plugs, unlike some new cars that require a wheel to be removed. I use a small wire brush, I get them in packs of three at O'Reilly for a couple dollars. Also some carb cleaner, good rubber gloves with big cuffs, safety glasses, and a disposable P-95 mask. I have a small ratcheting torque wrench set for spark plug torque per FSM, with a socket and extender. I pull one plug at a time, blast it with carb cleaner, give the tip and electrode a good brushing, blast it again, wipe the threads, and reinstall. Takes about 10 to 15 minutes to clean all the plugs if you're not in a hurry.

 

If it's not vacuum leak or fouled plug, or misplaced plug wires, that's good information, then you can rule that out and check other things.