Fixed.

I don’t know what did it, though.

I pulled the residual pressure valves out of the ZX master cylinder, but I also change from Nabco to Tokico reservoir caps. They have a slightly different design and there was a theory that the MC might be pulling in air from the back seal if the caps don’t let air in. I also had an extremely slight leak at the junction between the front brake lines where the OEM bias regulator used to be. And I bled the system again.

So who knows. Could have been any one or combination of those, but I can screech the fronts now, which was not possible before.

Now to get the bias right.

I was having some major tuning problems up until today.

After pulling the vacuum and plugging the port, setting the timing to 7°/750 rpm per the 240z FSM gave me a wild amount of backfiring when cruising or accelerating at partial throttle from both the carburetors and the exhaust (WOT was fine). Setting it to 34°/3,000 rpm gave me an idle at 24°/950 rpm, so the car would not start. I took it back down to 12°/800 rpm just to get it running again.

I had been all over the place with this trying to dial in my jetting, but the mis/back firing was still happening whether I went rich or lean.

I started to wonder if it was a problem with the weights in my distributor. It’s an e12-80 that was rebuilt by California Datsun. Everything worked as expected when I received it, but I didn’t check the value on the weights or their springs before I put it in because it’s a ZX distributor in a ZX block with a ZX head and he didn’t claim to have modified it.

Long story short, I messed with every jet option I could set up and finally landed really close to what the Mikuni manual recommended in the first place: 140 main jets (manual calls for 145), 200 air jets, 52.5 pilot jets (manual calls for 57.5), and 0.45 pump nozzle. The mistake I was making was mentally focusing on the main jets too much.

I’ll read the spark plugs after I put some miles on it, but I smells much cleaner than it was before I started messing around, the misfiring and backfiring under load has stopped, it starts immediately, and it’s damned quick.

Now to fine tune the idle speed, check my fuel pressure again, and sun the carburetors.

What a saga (although not as bad as the brakes).

Edited September 7Sep 7 by Matthew Abate

Progress is good!!

Anyone know what the hole circled in the photo below is for?

I thought it was for the choke cable, but apparently that’s on the passenger side in 1973 cars. Something for an automatic transmission?

1 hour ago, Matthew Abate said:

Anyone know what the hole circled in the photo below is for?

It's the drain hole for the factory air conditioner that was never offered on the Export market cars, only on Japanese domestic variants.

Curious what the reasoning was?

49 minutes ago, Yarb said:

Curious what the reasoning was?

"Thanks Mr K!"

/jk

I would imagine it was a matter of cost, weight and complexity (both in hardware and in fit/no fit building and ordering).

The struggle in keeping weight down for some markets was something chief engineer Hitoshi Uemura often mentioned in his stories about the creation of the S30-series Z, so it may well have been a key factor.

Nevertheless, the aircon-related details were built into every bodyshell, as well as the basic design of both RHD and LHD heater/fan units.

Just in case you haven't seen it, here's a factory document showing the system as fitted to Japanese (RHD) variants. You can see the hose and grommet that go in your drain hole:

Another mystery hole:

Anyone know what this port in the red circle is? It’s an F54 block. I’m hoping it could be repurposed for an oil return line from an Air/oil separator.

That is a coolant drain for the block.

3 hours ago, Terrapin Z said:

That is a coolant drain for the block.

Bummer. Looks like I’ll be having a port added to the aluminum pan.

In other news, I added a right side mirror (replica) today.

Getting it to match the left side was simple. I traced the contours and the holes for the left door onto velum and retraced those onto painter’s tape I had on the right side door.

After quadruple checking the measurements and making some tweaks I used a stepped drill to make the holes (28mm and 9mm).

Bolting it up with the window in was tricky until I remembered that the stud in the mirror can come out, which lets you thread the nut onto it and pass it up from the inside. I positioned the reinforcement plate first using a really long bolt with a flange washer on it as a threading tool.

Getting it perfectly matched to the left side means the visibility it provides is meh. Because it’s a replica that uses the left side ball joint it doesn’t turn in as much as I would like, so I’ll have to get used to looking further out and less behind me than I’m used to. Good for blind spots I guess.

Edited September 16Sep 16 by Matthew Abate