gundee

I think we have been through this before several times. The cylinder head needs to get pulled to see what the deal is with #4.

Been using Pertronix ignition and coil on my 240Z for about 20 years now. Works excellent.

I sent you a message.

I never knew he was moving to Spain. If he has his car in Spain now, it may be easier to find Z help than when he was in Panama.

Wires got crossed alright. In this threads software.

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I use manifold vacuum on my 240Z. Unplugged it is set at 10 degrees BTDC. When plugged in the timing jumps to 17 degrees BTDC. Perfect.

Here are the photos of a broken valve guide I was looking for. They can also be just cracked and allow alot of oil into the cylinder. A distributor will not change anything going on with yours.

Hasn't #4 plug been an issue from the start? If mine I would pull the head. Need to check the valve guides on the cylinder. On occasion (although very few) a guide have been found to be cracked right at the head. I had a E31 head with a cracked guide and the plug looked just like that. If they replaced the guides when the head was rebuilt, they can break one if not careful. Was the valve seal replacement a head off replacement or head on replacement.

I have used the pertronix ignition with 1.5 ohm coil and ballast resistor. Worked just fine. No issue.

I do not understand needing a choke on for 1 or more minutes. In that climate where you live. Use to start only if needed then shut off. If that was my car I would have a radiator shop test and recore it if necessary. I had to do that on mine. But now you can buy aluminum radiator replacements for 240Z's. It may be cheaper to buy one of those if the old one is bad. You also may have one of those old style water pumps with impellers that rot away and cannot move water anymore. You want the better type with cast impellers. Cooling systems should be in perfect shape in your climate.

Remove the choke cable from both carbs. Make sure the jets are in the fully up position. Drive it. See how everything goes. That eliminates any issues with the choke.

Yes drive it without if you want. No issue at all. I always removed mine when I autocrossed it.

It does sound like the chokes may be stuck open. This can happen if the screw for the linkage to the choke tube is too tight.

Is this just sudden in one day or a couple days?

I have this neat tool I would love to test number 4 with. Spark KV, Burn KV, Burn time in ms.

Seeing as how this is an earlier California Datsun head, its time to pull it. Check the valve guides and any evidence of oil coming from the head gasket.

Plug wires are likely fine. Under load is when they can break down. His issue is at idle. Under load he says the plug cleans itself up. Hopefully the issue is in the head and not the bottom end. Would be nice if it were just an oil seal.

Any guesses on sale price? https://www.barrett-jackson.com/Events/Event/Details/1970-DATSUN-240Z-271091

I'm curious. What paint colors did BRE use for the red car?

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I think you have been running that thing way too rich. Lean that thing out more.

Just start with 2 turns down and slowly adjust where it runs real good. I cannot imagine why you would want more then 2-1/2 turns. When you like how it runs, stop. Don't worry about what a plug looks like. Just enjoy it. You want your car to run good in traffic like you want. If it does that, your good.

That carb setting seems too rich from all the manuals. Will it run better on 2-1/2 turns? Its going to be how it runs best now. The plug look would not bother me.

Also have Mikuni set up. Had to trim the manifold some to clear the thermostat housing. Pretty common on these. I am not a fan of your choice of head studs. Some of those are too short for my liking. Same with the Mikuni studs. Just too short IMO.