Barefootdan's 280z Build

[Barefootdan]

I took apart the rear suspension again to loosen it all up. I was sure to tighten in the correct order and with the weight of the car on the suspension. I feel that this did help quite a bit! Although, I am not sure if my eyes are playing a trick on me or what, but I think I still see some toe happening. I may need to do a quick and dirty toe measurement with some plates to get a better idea! But for now I am moving on until I can get my hands on new wheels and tires.

Other fiddling I did was fixing my fuel gauge. It was always showing empty and never even budged when I turned power on. I started to diagnose the wiring and was just about to pull the gauge when I found a good post suggestion. Grounding at the connector near the fuel tank will simulate a full tank of gas. And funny enough when I did this, the gauge started to come to life! It was definitely sticky and jumped across its sweep until it came to Full. I think it just needed some OOMPH to get it moving 🙂 Glad to see my fuel amount now!

[Barefootdan]

Holy smokes time flies. Been so busy lately and havent had much time to work on the Z. Arizona summers suck the fun out of working on a car. Also moved from AZ to CO and still getting settled in. The Z made it here in one piece (via delivery of course!). Do carburetor jets need adjustment from altitude? I gained about 4K feet of elevation between Phoenix and Denver. 

[Patcon]

I would say yes

[Mark Maras]

My 71 Z roundtops were adjusted for near sea level. When I took it up to Timberline Lodge on Mt. Hood (app. 5000') I had to lean the carbs out a bit to keep it from missing. I noticed the miss started at just over 4000'.

[Barefootdan]

Dove into restoring the dash this past couple of weeks. It was destroyed by the Arizona sun. I didn't photograph the process too much because, honestly, I didn't have high hopes on it turning out well. 

Here is an old photo of what we were starting with:

Typical cracking for a Z dash, but boy was it brittle. My initial plan of attack was to get it off the frame and smooth out the ridges and cracks. But I was in for a nice surprise once it came off the dash frame:

Little did I know, the frame was holding together my now two piece dash 😅 The crack near the third gauge pod made its way entirely through the dash. Now I needed to fuse these back together before I could start any sort of work. 
I also looked into vintage dashes or other reproduction/professional repair options but the cost was just too much at this time. I told myself to try fixing what I have first, then if all else fails, a reproduction dash is always an option.

 

I grabbed some spray foam (loctite brand) and a couple strips of plastic to act as a "stitch" beneath the foam for the two pieces of dash to become one again. After "v" shaping all the cracks and smoothing out the ridges, I foamed everything together and used a jig between a couple of the mounting points to hold the two pieces of the dash in the correct spot. Note all my zipties in the photo below trying to make sure I didn't move the critical bond.

 

After a good 36 hours of drying, I finally mustered up the courage to undo the zip ties and see if everything held. And surprisingly, it did! Sturdy enough to bear the weight of itself from one side even. Success!

I now had a dash and no longer had dashes. I began to cut away at the foam and sand smooth with an orbital sander. It came out surprisingly well. The foam feel is excellent. Soft to the touch but firm enough to hold shape. I imagine this is how a good condition Z dash would feel. 

 

 

Unfortunately, this wasn't the end of my road blocks. If you look closely at the crack near the third gauge pod, my jig didn't take into account the transition between the two dash pieces. So while they are the correct distance from each other, the expanding foam must've made its way between the jig and the right piece to cause it to flare up slightly. Not a huge problem as I could sand, filler, and smooth it out. But something to note for future me.

I started to work the dash to ensure all nicks and minor cracks were taken care of. But it was endless...I would fix one, but the stress would cause another. I could cause a crack by just pressing down on the old foam fairly easily. Pricing out the cost of materials for filler, skim, paint, etc. I started to look into dash caps. 

I know, dash caps are not a good permanent solution. But who's project car is ever permanently done? 😉 

I did some research on peoples horror stories of warped caps or il-fitted gauges, glove box, etc. Some don't even match the OEM color. Luckily, every time someone brought up American Dash Caps, it was always positive. So that is the route I went here. Ordered up their full face deep cut cap and optioned to paint it satin black with SEM. 

Overall, it was a fairly decent cap. Some of the trimmings were rough, but easily cleaned up. They provided the silicone and an 18month warranty if you follow their steps. Simply apply the silicone 1/2" away from all edges and openings. It feels weird not applying silicone to the middle, but I bet this helps with expansion and contraction. I did need to sand a couple edges down for a snug fit. 

 

And here we are now! So much better than before. The photo makes it look very glossy, it is from the garage lights and just wiping it down after install. The true finish looks much more like the right side, satin. It is very close to the OEM finish in my opinion. 

While the dash was out I updated my gauge lights to white LED in a T10 socket. Almost half of my original plastic sockets were broken or missing tabs. Picked these up and the rubber socket allows for a snug fit with minimal trimming (of the socket itself, not the gauge).

 

I also cleaned up the dash wiring harness, installed a momo wheel I picked up while visiting in Japan! Cleaned up my gauges inside and out while I was removing the green lenses. Couldn't get that darn clock to work....

Everything is slowly coming together for the interior. Next up is some door cards and a new carpet kit. Not a huge fan of the one piece molded carpet. Going to look at Newark or Chester and Herod for my next kit. 

I'll leave you with a pic of my helping hand in the garage. She's much more willing to be out here in 40 degree weather as opposed to the 100+ degree Phoenix summers 🙂 

[Patcon]

That's good progress. I'm not surprised you had two dash pieces when I saw that crack...

Dogs are the best!

[Barefootdan]

Been tinkering around in the garage lately trying to tidy things up. I moved my fuse and bus bars from the original location in the passenger footwell to behind the glove box (with the actual box removed). Gives me easy access when opening my glove box while still being out of site. If I ever get vintage air, I can just slide it back down to the OEM spot and make a cover.

Did an oil change from the break in engine oil that was still in there. Then decided to dial in the carbs again for the new elevation. I dropped my pilot to 62.5 and it liked that a lot. But I could never get the crisp throttle response. I decided to take it back to basics and start fresh. I followed these steps and it felt much better. This is from a Mikuni group member, Duffy Mahoney, that was kind enough to share back in 2020:
"Mikuni Tuning 101

I’m not a guru, but it’s pretty simple. Also spelled out in the manual, which I would read a few times. You sort of chase your own tail doing this. Since each step affects each. I would have an rpm gauge hooked up you can see next to your motor. I use a timing gun with rpms visible to tune. Super easy! I did this whole thing 2x in a row. To make sure it’s perfect.

Two main things to tune. Pilot and Linkage

Pilot system (800-1500, I don’t know the exact range) rpms or so. This is the two thumb screws at the flange between the carb and the manifold. Pre-set to 2 turns out from down. These thumb screws change the air mixture for idle rpm range. Be very careful when setting these. I would gently turn each to seated. If you over tighten them it will ruin or damage the carb. Then back off 2 full turns. Factory is 2-2.5 turns backed out from lightly seated.

Linkage- This is critical to making sure the carbs are balanced. This is how much air the butterfly is allowing to flow at idle. It’s the shiny linkage on the side of each carb.

1. Get the car started. Two pumps on the accelerator. Then hopefully it will fire. If I was you I would hook up the choke system (Mikuni calls it the starter system). Once the car is warm and holding a idle you can start.

2. Set linkage first. This has to be done with either the dogbones (or called throttle arms) very loose or off. Dog bones are the small arms that attach the throttle linkage from the intake manifold to the carb throttle linkage. Each carb has a single throttle linkage with a set screw. Using a carb sync (air flow meter) try to get each to be the same (flowing) by small 1/8-1/4 turns. I would shoot 800-900 rpms for each to be balanced at. This is with the engine warm. Basically you are trying to get each to be sucking the same amount of air at idle. This needs to be done before you can get the pilot system done.

3. Set pilots (Total of 3) The goal is to tune each carb to the highest rpm possible. This is can be done with the linkage system on. Basically start at the carb close to the driver and using tiny turns on those thumb screws. You will notice a bump in rpms by turning either clockwise or counterclockwise. So carb 1. Do a single side of the carb. Turn it till it will maintain the highest rpm possible. Then do the other side of the same carb. Once one carb is done work your way through every carb. When I did my car I gained almost 200 rpms by doing this. It’s pretty interesting. I would turn and the car rpms will climb then eventually it will will go lower. Then back that set screw till it maintains the highest bump in rpms.

4. Now that the carbs pilot system is balanced you will need to set desired idle rpms again. I would ask Rebello for what rpms he suggests. But I would guess with your heavy cam you will want 900+ rpms at idle. So again with dogbones off or very loose. Turn each throttle linkage set screw counter clockwise or ccw till the desired rpms are achieved. I would do this pretty slowly on each carb. Matching turns. Like 1/4 of a ccw turn on each. Then using the carb sync match each carb to be exact and are sucking the same amount of air.

Then after this is done I would use a AFM to see if you need/ want to change jets. But I bet it will be a blast to drive by just doing this. If the dog bones aren’t loose enough during tuning you will have bad results. Since setting idle will slightly affect other carbs (I made this mistake).

Hints:

If the car doesn’t want to keep an idle before you start this you can give the linkage a bump. Give each throttle linkage a 1/8-1/4 cw turn then see if it will maintain idle. I set these but it’s a guess.

I set the butterfly’s. Which is one the hardest part of the rebuild. Basically each carb has 2 brass butterfly. Each has an infinite amount of movement. My goal is to get each to allow the same amount of light to pass. But it’s extremely difficult to be perfect. If in a super rare situation you can’t get the carbs to sync up. When can chat about resetting those butterfly’s. I’m 99% sure you will be fine.

Each Mikuni Carb is basically 2 carbs. So when tuning think that they are separate but connected by the throttle shafts to the butterfly.

Floats

You can adjust them on the car without removing them. You measure down to the fuel on each carb via the jet block holder and either raise or lower the float adjustment until you get a satisfactory level. The manual has a fuel level set point. The S5 Mikuni have external float adjustments (kidney bean shaped part) Older mikuni’s don’t and you have to pull the cover to adjust the float level."

 

Hopefully members here find this as useful as I did. 

One piece this left out was the accelerator pump position. There are three spots on the PHH you can set this to and it effects that initial tip in for throttle. Of course, this is where my problem was! Two of my three carbs were missing the cotter pins, so no wonder I was getting a massive bog. I used the middle spot first and it did help. Moved it to the third (highest) spot and it improved even more. This is where I left it. I'll dig into it when I get street time to see if I need a different size or anything to see even more improvements. 

 

My next project has been redoing my throttle cable and linkage. Not a fan of how I set it up on my first pass. While making new brackets, I was keen on looking into the design of throttle pulleys, or cams. Its interesting that most of the automotive world uses a fixed radius pulley, while it is very popular in the motorcycle world to use varying radius pulleys. Probably not as noticeable in a car, but a fun project nonetheless. 

I mocked up a "baseplate" for the throttle cable to attach that will allow me to slide in different pulley shapes. Here is the baseplate:

 

Then the baseplate, plus a pulley. Standard single radius in this example:

Varied Radius. Starting at 20% larger for the first portion, then dropping:

 

I have a couple in-between curves as well and curious to see if I can tell a difference in the real world. I wanted to keep the overall length within a few millimeters as to not need a new throttle cable for each iteration, but this did limit me in my overall curve shapes. There will be another baseplate, not shown here, that will sandwich the pulley to create a channel that allows the throttle cable to ride in. Everything is connected to a flanged collar that finally locks to the carb linkage.

 

 

[Patcon]

I am not sure how those profiles you designed would work in real life, but I think I would want a varied radius to have more resolution at lower throttle positions and less near WOT.

[Barefootdan]

Yep! Thats the thought process for making these. Hopefully by using a larger radius during the first half of the pulley, it will give a somewhat noticeable increase in throttle modulation off idle. Then, it ramps down quickly for high throttle inputs. 

[Barefootdan]

Got around to getting some new tires on the Z and took it out for a cruise around the block...this time without the constant worry of the dry rot tires leaving me stranded! It handles so much better and drives way smoother, who would've thought 

No overheating issues, solid oil pressure and voltage. The Koni struts need some additional adjustments to get the ride where I want it. 

One thing that I need to fix is the speedometer reading. It is reading nearly double what my actual speed is. Tested it with some neighborhood radar readings to get a baseline. I looked up the issue but most people are off by a few mph's due to tire size, diff ratio, etc. But I am way off, double or nearly so. Any thoughts on whats going on here?

[siteunseen]

If it was slower I'd say stripped groves in the plastic cog but being twice as fast???

I'd pull the connection/housing out of the transmission and give it a good look over. That's the easiest thing to do that I can think of. Good luck.

And it's the same height as the fill hole so you won't loose any fluid. Jack it up from the passenger's side to move the oil over even further away.

 

Edited March 7, 2023 by siteunseen

[Barefootdan]

I'll give that a shot. I think it also has something to do with the needle placement on the gauge itself. As soon as I start moving it jumps to about 20mph. Might need to reseat it in the correct spot.