74 260 Hesitates/runs poorly above 3500rpm in 1st and 2nd after car has heat soaked - runs great for first 30-40 minutes

[Kcusi]

74 260z with round tops Car was 'restored' around 15 years ago and mostly sat, and had a 'tune up' around five years ago. its been in my possession and I am finally getting time to mess with it and drive it.

THE PROBLEM - After the car reaches operating temp, it will run and drive fine for another 20-30 minutes. Pulls great through 1st, 2nd, and 3rd, 4th feels crisp and responsive as well. Then, suddenly after enough time has elapsed, I accelerate hard in first or second and starting right around 3500rpm it will...stutter?  and it wont clear up. Third gear is very smooth from 2-5k, I haven't tried a pull that high in fourth because...well, I haven't, but it drives well/is crisp/responsive in 4th as well when the problem is occurring. 

EDIT: maybe I wasn't paying close enough attention, it does seem it happens a little in third when the problem is occurring, it just isn't nearly as noticeable and not nearly as consistent. 

Through multiple videos and just trying things, ive got it running rather well with the exception of the title. Cold start/hot start not a problem. Mixture is a tad on the rich side (going by the lift the piston a tad and the idle will rise, when I take around 1/2 a turn of fuel away from where they are currently set it will respond the 'correct' way. It feels better where it is set ) and the carbs are balanced. Car has a new coil, cap, rotor, (had spares with the car, so im not sure where they originated, some not out of box new) plugs, full exhaust, current carb oil is atf. Fuel coming out is clean, 4ish psi, plugs look good, I have played with timing and it seems to be happiest around 10* of base timing. (i've also seen conflicting info on timing) The motor was rebuilt at some point previously, so i'm not sure if the compression ratio has changed by enough to matter due to machine work?

I may need help identifying the distributor/ignitor combo. It's no longer points, looks like a 280dist. With an aftermarket ignitor possibility?

Plugs look good.

Happens with more than one ignition coil.

Plug wires all check well cold and hot, wiggle them around, no open condition.

Ballast resistor still in place. Is this an error? I've read conflicting info and it has a 12v coil on it as well as some type of non points (cap, rotor, ignitor) style distributor on it. Should the resistor be removed?

I can't identify exactly when it happens but it is rather sudden. It's not a condition that gets worse as it warms up. It will be fine, fine, fine, and then bam there it is. I'm wondering if it's electrical (ignition system specific) related. I'm leaning that way because it is a sudden change. Similar to if you had a bad coil or bad injector. The car will run fine until that component reaches the "critical temp" and then the error occurs and doesn't go away until it cools down. That all being said I'm not sure what/where to check for an error once the problem is occurring.

This is also my first post here, so hello! 

Edited February 12, 2023 by Kcusi
Updates

[Zed Head]

5 minutes ago, Kcusi said:

I may need help identifying the distributor/ignitor combo. It's no longer points, looks like a 280dist. With an aftermarket ignitor possibility?

Post a picture.

260Z's had electronic ignition.  They were the first Z's to get it.

[Kcusi]

14 minutes ago, Zed Head said:

Post a picture.

260Z's had electronic ignition.  They were the first Z's to get it.

Is this a stock 260 distributor? I guess now thinking it was a 280 doesnt make sense as there's no ignition control box?  

[Zed Head]

Yes, that looks like the stock 260Z distributor.  @SteveJ would know for sure, he has one.  It is electronic.

The ignition module is under the glove box on the kick panel.  Looks space-agey with aluminum heat sink fins.

Watch the tachometer needle when the problems happens.  If it is jumping around, not following engine speed, that's a sign of a failing module.

[SteveJ]

@Zed Head is correct. That is a 260Z distributor. It never had points.

The TIU should be mounted in the passenger footwell. It looks like this.

It sounds like you may be thinking of the 280ZX distributor that has the ignition module mounted on it. The 280Z had a similar ignition set up to the 260Z.

YES, there is supposed to be a ballast resistor.

I suggest you download a copy of the factory service manual from here: https://www.classiczcars.com/files/category/12-260z/

Read through the EE section on the distributor and ignition. It will have information on the timing.

As for the title problem, I can't tell by the description, but I would start looking for where you could be losing spark energy, such as through bad plug wires or bad distributor cap.

Also make sure your plug wires are fully seated into the base of the terminal on each cylinder and coil post on the distributor. A few months back I was looking at a friend's 240Z with Pertronix that was not going above 3,000 or so RPM. I started going over each part in the ignition and found a plug wire that was not seated properly. It did not show up as a problem with the car sitting still, only while under load. With the wires seated properly, the car ran like a scalded dog.

 

 

[Kcusi]

Sounds good. Thanks for the input so far. I will check out the timing specs.  

The tach responds accurately to engine speed when the problem is occuring.

Stevej, I understand what you're saying. I will check everything again piece by piece again and see if I can find something. I did manipulate the plug wires and coil wire when I had a meter on them with no luck. I'll post back if I find anything.  

Edited February 9, 2023 by Kcusi

[Patcon]

Another of SteveJ's tricks is to spray compressed air upside down onto the ignition module when it acts up to cool it. If the problem goes away that tends to narrow the problem down to that module. As they age they can act up when they get hot.

[Zed Head]

zspert's posts about the V-3 system might have some clues.  It would be great if he pulled them out in to a separate thread, but you can find them in this one.  Post #2141 if it doesn't click through.  There are two more somewhere before it.

p.s. has anybody noticed that the search function does not work at all?  Nothing, even if you copy the phrase exactly as it is in a post, Search does not find it.  "Did someone say V-3 kit" returns absolutely nothing.

 

Edited February 9, 2023 by Zed Head

[Patcon]

Also, what is the fuel system? Flat tops? Round Top SU's?

[SteveJ]

Just to make sure it was clear about what I was asking you to check on your plug wires.

 

[Captain Obvious]

3 hours ago, Patcon said:

Also, what is the fuel system? Flat tops? Round Top SU's?

Round tops.

Or I would have been involved at the start. 

[Patcon]

I missed that. I guess it was Obvious to everyone else ...😁