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Unstable idle/failure to run properly


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I haven't run my Z in about 2 weeks since I have been working out some electrical issues involving the burned out fuse box and being busy with some other things.

Today after I put in the 'new' fuse box and tried to fire it up, it(the engine) ran way worse than before. The electrial systems like lights, radio, etc worked just fine, however the car was very tough to get running, and when it finally started to turn under its own power, it had a very unstable idle (not really idle I suppose, since it required me giving it gas to keep it going at this bad rythym) that seemed very erratic... sort of like only 3-4 of the cylinders were combusting.

The engine would turn in this unstable rythym for only 10-15 seconds at most before it slowly died (with my foot pressing the accelerator, it would not start otherwise. The engine would not start without giving it some gas before this recent foulup anyway).

I checked the carbs, both pistons seemed to move freely: fall at the same rate and rise with the same force.

I checked the fuel filter, and it looked good.

Because the fuel flow and carbs 'seemed' ok to my novice eyes, I figured it must be an ignition problem (?) so I pulled off the distributor cap and noticed some carbon buildup on the rotor tip and the points (correct terminology? I don't have my manual on me ATM) inside the cap, so I carefully removed it with some fine sandpaper, replaced the cap and attempted to start her up once more. The engine idled with pretty much the same unnatural rythym before slowing down out until it stalled after about 10-15 seconds.

I will probably go to the parts store and buy some new spark plugs tommorow or monday and replace the existing ones. I'm not too sure when the previous owner replaced them, and i'm guessing this could be a part of the problem as well?

Could it be my ignition coil?

Could the needles on my carbs be partially clogged?

I was going to try to adjust my SU carbs, but upon reading the segment in the FSM, it called for the use of an air flowmeter which I do not have. Any hints? Just buy one and follow the instructions to the letter? I could tell by the smell of the exhaust before this 2 week break that it was running rich anyway.

Before the 2 week hiatus, it was something of a PITA to start anyway, but once I got it idling, it would eventually smoothen out and idle fine with a little gas and choke, then none was needed for it to idle once it started to warm up.

I am a car mechanical novice, as you may be able to tell, but this is all a great learning experience for me. The manuals are great for certain things, and I have read over most of the related material, but I can learn a lot more from hearing from you guys with a lot of experience. I would like to get my car running and legal again before summer and have already fixed a number of things, many of the repairs thanks to advice I got here or read about in the archives.

Any help or advice you guys could give me would be MUCH appreciated!



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Thanks for the reply,

I am pretty sure I didn't, I made sure not to move anything that would affect that and cleaned the rotor while holding it still. I placed the cap back in the same position as before. The engine ran the same before and after I cleaned out the cap and rotor.

This was the first time I have opened my distributor up since I got my Z a few months back.


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Since you did remove the cap..I would check the wire from the capacitor that hangs outside the dist. to make sure it isn't shorting out..check for fraying on the wire. If in doubt replace it (cheap). That may have been your problem all along. I don't remember you saying you checked the spark gap or not. That should be set (and clean the points with a point file or super fine sandpaper -2000 grit) to specs. If the points look very bad or crusty then I would replace them as well.

Hope that helps some.


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Take a look at the connections at the coil and the resister actually look for a proper ground form the engine to body. Do check the points and if they are pitted replace them and the condencer. I would pull the plugs and see if they are burned , most likely they are oil soaked and or fouled, clean them or replace. :classic:

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I would replace the cap/point/cond. also.As they wear it obviously increases the distance between the contacts.Sand can clean them but wear is wear.Just a note,I have a master mechanic friend that says sandpaper is not advised.He says the adhesive that holds the sand to the paper can stick to the part you sand.As it gets hot and burns it becomes an insulator.I use a metal diamond nail file I took from my wife for points and a wire brush for plugs.

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