Mark Maras

"Do it in a Datsun"

Before proceeding to valve guides, I need you to test the #4 plug (use a new plug) against a ground by turning the engine over with the starter. That will ELIMINATE a possible electrical cause of the fouled #4, then we can move on to oil fouling. But while I'm thinking about it, how much oil does the engine use in around 1000 miles or 1600 kilometers?

Yeah, Put a hotter plug in #4. It's a band-aid but it may buy you some time until we discover WTH is going on. Is the dark color on #4 plug oily, smell like fuel or is it dry carbon? I'm beginning to suspect a bad valve guide or valve guide seal on #4 if the colorization is oily. Looking at your latest pic of #4 it looks like the plug is trying to fire (clean near the center electrode) but is being overwhelmed by either fuel or oil. Fuel can be crossed off the list so it is likely oil. One more test please. Pull #4 plug, put the wire on it and ground the plug (With an insulated gloved hand) while turning the engine over with the starter. Watch the spark and note the color. It should be bluish, not yellow and you'll probably be able to hear it.

The early 240s valve covers I've cleaned (usually with lacquer thinner) had no coating. I believe that's true of the later ones too.

Ok, the closed throttle explains the low numbers on all of them, however it still doesn't explain the misfire on #4. Back to the simple things. Are you absolutely sure the number four wire has been securely attached to the plug. It should have the same noticeable click as the others when you snap the plug wire onto it.

@jalexquijanoWere those readings with the throttle wide open? Also before or after checking the valve lash?

Yes, and after they've been reset another compression test would be helpful to rule out low compression in #4.

That has been my understanding. I hope I haven't been wrong for 50 years. I once owned (before Zs) a dragster (BB/GD) with a blown (671) 327 small block chevy. The center electrode was recessed down in the porcelain on the plugs that came with that engine.

The switch in the upper rt. corner is the antenna switch from an early Z that had the AM radios like my early 71. You may be able to use that existing switch if you can source an early faceplate. I don'r recall when the change was made but it does seem a bit weird that you have an old switch in a 73.

Have any of the #4 plugs you've pulled in the past had no gap? Is it possible that you dropped the spark plug or bumped it against something that closed the gap previous to installation? If it were mine I would re-gap that plug, install it, disconnect the coil wire and turn the engine over with the starter for a couple of revolutions. Then pull the plug and see if the gap is closed again. If the gap is OK, replace that plug with a new one and take it out for a test run. If the gap closes again take a pic and report back. The resistance readings on the two wires look OK to this non-electrician.

I don't see how the distributor can be bad. The coil wire leads to the center of the rotor, which spins and distributes the energy to the contacts in the cap, then to the wire, then to the plugs. If the problem is electrical it has to be somewhere between the #4 internal cap contact and the connection at the plug. (you did check to see if the screw on connector on the plug tip was tight, right?) I think the best way to test the resistance is to remove the cap with the wires intact. Check the resistance in all six as an assembly by touching one probe to a contact inside the cap and the other probe on the sparkplug contact inside the spark-plug boot. Check the resistance in all six. Actual numbers aren't as critical as major differences, especially in #4.

Looking carefully at the pics, I think I may see the carbon trail. The horiz. flat #4 boss that holds the contact has a very faint vertical line on it, then looking at the next contact down in the pic I see what appears to be another or the (kinda wavy) same line under the top of the lid that runs down from left to right. The carbon trail that I originally discovered on my 521 was very faint too. Do you have a volt-ohm meter, I don't remember.

I've seen carbon trails inside the cap from one contact to the contact next to it that caused a misfire. The carbon trail (track) looks like a line drawn with a pencil. The cause was a poor spark plug wire connector. The path from one contact to another inside the cap was an easier path to complete the circuit than jumping the bad connector in the spark plug wire. @jalexquijano Have you ever compared the resistance in all the spark plug wires with an OHM meter? They should read about the same as each other. No need to pull them from the engine. Just disconnect both ends and stick a probe in each end.

Those are great compression numbers. Did you ever try removing #s 3 and 4 spark plug wire and switching them to see if the problem moves to another plug along with the wire?

@jalexquijano I remember a compression test from a while back but I don't remember the results. Could you post them again?

I'd try a hotter plug. It won't tell you what's wrong but it might buy you some time.

Glad you got your starter problems resolved. I wish I could give you an opinion on the spark plug non-foulers but I don't even have an educated guess. I'm not familiar with the product at all. It's cheap and I doubt it can do any harm. I'd be interested in hearing about any change if you try them. Anyone else want to chime in? Have you tried all the things that @AK260 suggested in post #15?

I loved Westwood too. Down that short hill, pulling multi G forces at the bottom was the most fun for me. Lap after lap, going down that hill, I kept believing I could enter that left hander faster than the previous lap. That theory worked well for a few laps until I went off on the left turn exit. Regretfully, I never felt like I mastered that off camber downhill right hander. I loved tracks with elevation changes.

Submerge it in CLR for 24 - 48 hours (Thanks @wheee!). It will come out looking nearly pristine.

A good many years ago I was headed up I-5 (relatively flat section) going a good 75ish mph when suddenly my 71 240 slowed to 45 mph. It was running smooth and being a few miles from my folks house I decided to try a few things, I pulled the choke, no change. Kicked in the clutch and revved it to 6 grand. Let the clutch out and it would not go faster than 45. Shifted into third, no change. Shifted into second, no change. Got to my folks house doing 45mph and I told my Dad (an old school logger) about my car woes. He kind of chuckled and said the engine wasn't getting enough fuel. I countered with the damn thing will rev to six grand but then he explained an engine under a load consumes more fuel and it won't go any faster , no matter what gear I was in because it only had enough fuel to pull the load that speed. It would rev fine because there was no load. Our temporary solution was remove to the underhood fuel filter and blow it out in reverse flow direction. I drove it home the next day (75ish) and had no trouble. Replaced the old filter after that and never experienced the problem again.

The major concern at this time is the float levels. I'd work on that first. The needle installation looks OK.

I agree. Any of the three ways are a piece of cake compared to removing and replacing those parts on most cars.

He won't be the first Gov. official to make a one way trip to Walter Reed.

Correct, 1 turn = 360`. I'm not sure what you want to do to one needle. The piston drop and lift test seems to have confirmed the needles aren't scrubbing the nozzle ports. Just looked again. I think I see what you mean. The top (base) of the needle looks like someone wrestled it out of the piston with new sharp pliers. It also appears to be bent or is that just my eyes? I don't believe there's a good reason to hook up the choke cables if you don't need the choke but that could be a too rich symptom. The piece of flat bar linkage that pulls the nozzles down needs to be installed.

An 8" rod is impressive. Perhaps we've discovered the reason for no pics.