Datsun 240z weird startup

[Alex240z]

Hello everyone,

I have a  1971 Datsun 240z I’ve had for a while. Unfortunately for me when I bought it the head gasket was blown and rusted the cylinder wall so the engine was seized but I was lucky enough to obtain an engine off a running 1972 240z. My 1971 didn’t come with a harness so I also got one from the same model and production month as mine 1971/6 so it fit nicely In my car. 
 

Another unfortunately is my datsun is idling weird. I wouldn’t even consider it to be called “idling.” The mechanical pump is taking in fuel, the ignition coil and distributor is working because I’m getting spark, the engine cranks over and starts when I put the key all the way and hold it on start in the ignition switch. However when I let the ignition switch move to the on position the engine dies. Another weird thing is that when it’s on start the engine reeves to the moon and back. It appears to me that it’s an electrical issue but I’ve already check the harness throughly so I’m not quite sure what’s the issue. The only issue I can really think of is maybe a vacuum or air leak but not quite sure what it could be. None of the connectors or fuse box is running hot so no fires thankfully. Some other stuff that were weird that comes to mine are

voltage regulator that I bought has six wires in its plugs but the connector plug only has 5

oil pressure switch isn’t connected

dont have a choke cable 

The harness I bought didn’t come with fuseable links for the starter and alternator. They just soldered some high guage wire instead. 

I don’t have any photos at the moment because it’s late where I live so when I get the chance I’ll update this thread with some photos so it’s easier to explain. 
 

thanks,

alexander 

 

 

[dutchzcarguy]

21 minutes ago, Alexg280z said:

However when I let the ignition switch move to the on position the engine dies.

Thats a failing resistor in your ignition circuit.. for a test you may shortcircuit the resistor you find near your coil..  I bet you it will stay on!

Get yourself a new resistor, or repair the failing contact on the old one!

[Alex240z]

9 minutes ago, dutchzcarguy said:

Thats a failing resistor in your ignition circuit.. for a test you may shortcircuit the resistor you find near your coil..  I bet you it will stay on!

Get yourself a new resistor, or repair the failing contact on the old one!

Interesting. I’ll check it out in the morning. Any idea on the high reeving? 

[dutchzcarguy]

50 minutes ago, Alexg280z said:

dont have a choke cable 

Maybe the choke is "hanging" thats causing the high rev.  could be lots of things.. high rev can also be caused by a vac. leak..  If you think you see a leak spray some brakecleaner on it, if the rpm changes.. thats a leak.  Watch out that you don't burn down the car, don't do it on a hot engine. take precautions..

[SteveJ]

3 hours ago, dutchzcarguy said:

Thats a failing resistor in your ignition circuit.. for a test you may shortcircuit the resistor you find near your coil..  I bet you it will stay on!

Get yourself a new resistor, or repair the failing contact on the old one!

It could also be the ignition switch itself. This is why you need to own and know how to use a voltmeter. Check the voltage at the ballast resistor with the key in the ON position. One side should have voltage. Heck, even a test light would work for this.

[Alex240z]

2 hours ago, SteveJ said:

It could also be the ignition switch itself. This is why you need to own and know how to use a voltmeter. Check the voltage at the ballast resistor with the key in the ON position. One side should have voltage. Heck, even a test light would work for this.

I forgot to mention that I bought an aftermarket switch from Zcardepot but I’ll give it a try. Thanks again. 

[Mark Maras]

 I agree with the ignition switch being the cause of it shutting down when it switches from start to run however, that doesn't explain the high revs. High revs are usually caused by excessive air not excessive fuel. Example, one can't cause sky high revs by adding choke. I'm going to start with the obvious (Sorry Cap'n) Do you have both carb return springs connected. The ones that anchor to the heat shield? Vacuum leaks, while a possibility, usually affect low rpms. I've not seen vacuum leaks cause sky high revs.

[siteunseen]

Can you look at the butterflys in the carbs? They should be closed. I think it's something in the linkage too if you've been working on that area. 

Here's something that I had out of order that caused high revs. This is a picture of the right way by the way.

Oh yeah. Now my turn to play Captain Obvious. If you put a new ignition switch in maybe you got a wire in the wrong spot?

Edited February 25, 2021 by siteunseen

[Alex240z]

2 hours ago, SteveJ said:

It could also be the ignition switch itself. This is why you need to own and know how to use a voltmeter. Check the voltage at the ballast resistor with the key in the ON position. One side should have voltage. Heck, even a test light would work for this.

After a quick search of ballast resistor online I see the problem. I don’t have one. 

[Zed Head]

[Captain Obvious]

This is awesome... I don't have to even get involved!!     

[Jeff Berk]

Just a precaution, either get new fusible links of the correct amperage (color) or install some breakers. The old wiring on these Z's scares the hell out of me.