HELP! All Mechanical Eliminated- Wont rev past 4K

[Seanw987]

Brand new MSA 6-1 header and new MSA exhaust.

Fuel Tank was treated and lines are clean, new filters,pump,sending unit, and All of this was bypassed at the carbs, with elec. fuel pump and separate gas tank(5 gal). same issue. Im thinking Electrical. Maybe something in the secondary ignition circuit.

Original owner mentioned that the car had the same issue 18 years ago when it was driven last but he didnt seem to mind or care to address it.

Now the new 2.8L motor is doing the same thing.

distributor has been replaced.

[ChrisZ]

I still think it's a timing problem, please list all that have been done /swapped.

Have you measured the fuel preassure at the carbs, what kind of carbs, does it back fire, what is stamped in to the distributor, do the rotor line up with cylinder one on the distributor cap at TDC, are both rockers loose on cylinder one at TDC, if you take of the distributor do the oblong on the drive point 11.25 at TDC.

You have to start all over, in order to make sure that everything is spot on, read this http://www.xenons30.com/files/FSM/1972%20240z%20FSM.zip (got you this time Stephen)

Chris

[whamo]

When you note that it will not rev past 4k, is that in neutral with no load, or driving in gear? Is the iginition system completely stock? including tachometer? how about your throttle linkage? Do the carbs open completely with the throttle pedal?

[doradox]

The car won't rev past 4K. Carbs have been swapped, fuel system bypassed(for testing) coil, distributor,points/pertronix, all have been changed out, even the tach.

Wires to and from the coil and distro have been checked/replaced.

Sean:bulb:

So if you or someone else has properly tested and changed all those things then you have eliminated fuel and ignition.

I need to mention that these symptoms were also identically present when the car had the original 2.4L engine with stock components ie cam.

Sean:

Now you have eliminated the engine mechanical and any cam timing issue.

Brand new MSA 6-1 header and new MSA exhaust.

And now exhaust.

The cam is a performance grind and the car idles great and runs great up to 4K.

Any timing problem ( or throttle linkage problem) serious enough to keep you from revving past 4K would certainly effect your performance below 4K. Centrifugal advance should be all in well before 4K.

I'm thinking Electrical. Maybe something in the secondary ignition circuit.

So did you do this..

coil, distributor,points/pertronix, all have been changed out, even the tach.

Wires to and from the coil and distro have been checked/replaced.

Because that pretty much covers the secondary ignition system. Did you check cap and rotor? Air cleaners collapsing and choking the carbs?

You've eliminated everything that could be causing your problem so you need to start over and recheck all of it. Either that or a part you swapped out to do a check was bad in the same way as the original part.

Steve

[=Enigma=]

I had the same issue and it went away when I replaced the plug wires and coil. I did them at the same time so I can't which was the culprit in my case, and I know you already replaced the wires. Could it be a bad coil? have you tried swapping that out?

Edited March 1, 2009 by =Enigma=
added more verbosity

[beandip]

I know this is vary basic but have they checked the float levels? Obviously it is one of two things . 1. ignition 2. fuel . Ignition and timing fall in the same category. If the butterflys are opening fully and the floats are set properly, the vacuum dampeners are free and not sticking, plus if the Carbs are reasonably close in adjustment. The gas supply is alright , then it must be ignition . You did say that the cam timing was checked. What are you using for ignition? OEM points , ZX , Petronix , what? Do as Arne suggested and try and advancing the timing a little and see if there is any improvement . I am running 16* advance with a ZX ignition and my engine runs great. Don't go to that advance right off if you are running a different dist. than I am. Keep us in the the loop on this.

Gary

[ChrisZ]

He runs a Pertronix, but on what distributor, he should follow the FSM, like re building a motor, if all is spot on when done it should start right up.

What about the fuel pump, is that the right one, if the arm is to short or have the wrong bend it could also make it starve.

Chris

[whamo]

What about the fuel pump, is that the right one, if the arm is to short or have the wrong bend it could also make it starve.

Chris

The symptom does not sound like a fuel pump at all to me. If a pump is producing to little volume it should still fill the float bowls at idle and you should be able to freely rev the engine until the float chambers run low on fuel. Thats what mine did with a bad/wrong fuel pump. It would run/rev fine until the engine was under a high load for an extended period of time, thats when a low fuel supply will become evident.

[doradox]

The symptom does not sound like a fuel pump at all to me. If a pump is producing to little volume it should still fill the float bowls at idle and you should be able to freely rev the engine until the float chambers run low on fuel. Thats what mine did with a bad/wrong fuel pump. It would run/rev fine until the engine was under a high load for an extended period of time, thats when a low fuel supply will become evident.

Not a fuel pump at all is correct, especially if you read this...

Fuel Tank was treated and lines are clean, new filters,pump,sending unit, and All of this was bypassed at the carbs, with elec. fuel pump and separate gas tank(5 gal).

Emphasis mine.

He also says he's tried two sets of carbs with no effect. Anyway, any mechanic worth his salt would have introduced additional fuel with the engine running at 4000 rpm to see if it would rev out. A simple squirt of carb cleaner while holding your foot to the floor would immediately tell you whether or not it wasn't getting enough fuel to rev past 4000 rpm.

Steve.

[ChrisZ]

Yeahr, guys your probably right, it was just a thought i had.

Chris

[whamo]

I personally believe its the throttle not opening all the way. Foot pedal assy or throttle linkage bent, limited or maladjusted. Lift the slides, shine a flashlight down the barrel while someone has the pedal mashed and check the throttle plate open completely. Engine turned off of course.

[Trys_Hard]

The throttle is opening all the way. We did get his prior motor running past 4k, before we put in this new motor that he bought from Datsun-Parts, LLC. It was assembled with a hodgepoge of different year motor parts. We have now tried to advance the timing more with some success but there are still issues. Mike my partner has been working on Z's for 26+ years and this is definately a strange one. Just about every tip suggested here has been tried and more.