Mark Maras

I think it might improve it but I doubt that it would be eliminated. There's still something wrong and we're getting closer to the cause, I think. Reducing the gap would certainly allow it to fire easier. One could combine both ideas (maybe) and buy a hotter plug and reduce the gap. Who knows, it just might work. BUT, my decades of shade tree mechanic work tell me this is a very simple problem (unless it's Pertronix related) and I refuse (at least for now) to give up. I have the same feeling about this problem as the previous SU problem. Simple problem, simple fix. @jalexquijano Have you tried swapping #4 wire with another next to it? After swapping the two wires, warm it up, take it for a fun drive, bring it home and let it idle for a while. Let it cool down and pull all the plugs. That should be the next test. We're getting closer to the problem.?

@jalexquijano I'm proud of you. An improvement. Interesting that we're back to #4 looking worse than the rest. I think it may look a little better than before. Do you think that you could swap #4 plug wire with either #3 or #5, Length would be the only problem. Swapping #4 with another wire will allow us to see if the problem stays at #4 or goes to another cylinder with the wire. I'm interested in your thoughts on this. You're the one that improved the firing on #3 and #5 by (I'm assuming) checking and adjusting the connections. Can you think of anything specifically you did to improve it?

I like your wild arse guess. Now we need a Pertronix guru to walk us through a test procedure. Volunteers?

Speaking of old engine analyzers, my Dad used to check his plug wires by waiting until dark and spraying water (spray bottle) on the plug wires while the engine was idling. It was my first of many light shows to come. @jalexquijano Give it a try. You never know, it might turn something up.

Hi Charles. My decades of welding was mostly done on galvanized pipe and steel. I've experienced the symptoms of "zinc fume fever" (google it) many times. Along with a sweet taste in your mouth, it will give you the same symptoms as coming down with the flu. Headache, fever, chills, thirst, nausea, vomiting, chest soreness, fatigue, gastrointestinal pain, weakness and tiredness. (List is courtesy of Lincoln Welding). As you can see, zinc oxide fumes can make you feel pretty crappy. The good news is that the symptoms don't last all that long. By the end of a days exposure one goes home sick. Next morning the worst of the symptoms are gone. The effects seem to be cumulative. After a week of daily exposure, one needs the weekend to partially recover. I've not had much exposure to cadmium but you're correct in that cad. has much worse long term effect. Prayers coming your way. Let us know what you discover. Many of us are welding and plating on a regular basis.

Ok, If you've completed all the tests and found everything looking good put it back together with good (or new) plugs and take it for a run and then let it idle. I'm hoping that you've improved the connections while doing the tests. Let us know.

Ok, Now with the wires connected to the plugs and cap, measure the resistance from each of the contacts inside the cap to the center electrode on each spark plug.

Good job but, no ride yet. Now disconnect the wires from the cap and connect them to the spark plugs which have been removed. Measure the resistance from the center pole on the bottom of the plug and the connector on the wires that goes to the dist. cap.

Ok, good. Now connect the wires to the distributor cap and measure the resistance from the contact inside the cap to the spark plug connector. see if the readings change.

NIRVANA!

Are you sure you're not leaving a bit of heaven. Donuts, good coffee, parts store across the street. I'd be looking for a nearby house for sale.

Measure the resistance in all of them. We'll start there. There are numerous videos on YouTube to show you how.

No. The fact that some of the plugs look good means that the coil is working fine. The problem appears to be in the distribution of the spark to all the plugs. That's why a distributor is called a distributor. The distribution of spark is handled by the the spinning rotor receiving high voltage from the coil then it distributes the spark to the contacts inside the cap into the spark plug wires. There are four connections on each wire that can give you trouble The connector that plugs into the cap. The connection of the wire to the previously mentioned connector, then we move down to the plug end. There's the wire to the connector and the connector to the plug. Any of those connections can cause a fouled plug. The test that I described earlier is to try to isolate which connections are bad. Grab a cold beer or two, your multi-meter, enough time to do it properly and have a go at it.

If I were that mechanic, I'd grab my volt-ohm meter first.

@jalexquijano We can't eliminate poor wires or connections until you complete the tests on all six. Three separate tests that includes testing with everything (cap and plugs) connected Then another test on all six with the cap disconnected, plugs connected, then a third test on all six with the plugs disconnected and the cap connected. It would be a good idea to do a fourth test on the wires only. No cap or plugs connected. I still think you'll find the problem somewhere in the cap (new), rotor (new), wires, or the wire connections. I think the carbs are close enough based on some plugs looking good. You've checked for intake leaks and found none. Compression ratio is OK. There's really only a couple of things left. Valve seals are a possibility (seals could have been damaged due to improper installation) but lets eliminate the easy one first. Try not to get too frustrated. WE will figure this out.

You could pack a spare set of round tops with you. Less energy to change carbs than pushing.?

I'd grab a volt-ohm meter and measure the resistance from the contacts in the dist. cap to the body of the spark plug. Basically, remove the cap leaving the wires plugged in. Next remove the spark plugs and plug them back onto the wires. One of the meter leads will go onto the contact inside the cap. The other meter lead will go onto the body of the spark plug. Measure the resistance in each of the cap, wire, and plug. When you find one with a lot of resistance remove the cap and measure the resistance in the wire and the plug. Then reinstall the wire into the cap and pull the plug from the wire. Then measure the resistance in the wire and cap. Ask if you have any questions. It's the best way to learn.

Sometimes you just have to go with the limited info and have faith that it will work out.

1100 rpms is a nice busy idle. That should help eliminate the plugs loading up. Watch your temp gauge. Things can get hot pretty fast at a busy idle unless your fan-or fans are pulling a lot of air.

I hope you've checked all the connections. Don't reuse any of the black ones.

You asked. Here's my gut feeling. It's based on what I'd do (if it were mine) to get your car back to a RELIABLE DAILY DRIVER. Honestly I'd put a stock engine back in it. Zs didn't like hot temperatures from day one and Nissan never did successfully solve the problem. You'd be a lot happier with a stock engine. My daily driver (summer and winter was a bone stock early 71. The most reliable, trouble free car that I've ever owned. Don't know what the availability of stock engines is in Panama but they're pretty cheap around the Pacific Northwest. Engine and shipping costs may be cheaper than importing a mechanic and an engine swap is very easy.

I didn't give up on #5. That plug looked pretty darned good, imho, having idled for a long time. I was just glad to see that all the plugs weren't black. It doesn't matter to me if the other five were black. The fact that at least one plug looked good narrows the problem down. Also, the original problem was always isolated to #4 until the dist was removed and reinstalled. Then #5 started doing the same thing as #4 did previously. Seems to me that moving the wires and or disconnecting them and reinstalling them is the cause for the #5 gremlin and probably #4 too. I considered valve seals too but the two dark plugs looked sooty not oily. I'm hoping that re-seating the wires will eliminate the misfire. With Alex removing and reinstalling the wires the misfire may move to another cylinder until all the wire connections are right.

Only if they feel loose. I've experienced connections that are too loose as well as connectors that were so tight that they wouldn't slip over the plug connection. Same thing with the dist. cap connectors. You'll have to assess each connection and determine if it's too loose, too tight or just right. I think we could call the just right connection the "Goldilocks Connection.

I agree you'll need a new set of plugs but installing them now and letting it idle without finding the problem is just going to foul a couple of new plugs. Check you spark plug wire connections either with a meter or by unplugging both ends and reinstalling them. Be sure that all the wires go into the cap and onto the plugs the same depth. Based on past descriptions of the problem I'd guess that the #4 wire problem is the wire to the cap connection. #3 could be either connection but I'm leaning toward the plug connection.

Do the test with the engine stone cold. We're looking for a poor electrical connection, or a bad wire or two. I know all the ignition parts are nearly new that's why I think it's a poor connection. When you installed the plug wires into the cap were you sure they all went in all the way? Same question applies to the plug wires onto the plugs.