Fuel recommendation for a '73 240z with rebuilt engine and SU carbs?

[Dadsun]

My Z seems to be running rich. I have swapped in the SU rebuilt carb set and adjusted as best I know how with the unisyn tool and mixer adjustment on the bottom. 

[Yarb]

Need a lot more info than what you have given. Pics, source of where the carbs were sourced etc. Anything you can add is helpful. Reasoning for replacing them etc etc.

[w3wilkes]

On the question of the thread title... When I had my carbs done by ZTherapy I did the tank and all rubber lines with new Gates hose rated for E85 if we're ever forced to go that way. Since I did the whole fuel supply front to back I've run nothing but ethanol free fuel which is readily available here in Utah. The car seems to be very happy with the ethanol free fuel.

[Dadsun]

Yeah, apologies for the sparse info.  Here's a thread on my conversion to the Paltech refurbished carbs.

This was to replace the original flat tops which were sorely neglected and of course problematic. 

 

[Dadsun]

Here's a pic from the last time I was adjusting them. Notice that I'm running coolant through the intake manifold. Some choose not to do this, right?

[Dadsun]

Since then I've swapped in the fuel rails to go with the round tops. I run 91 octane because it's the only ethanol free gas around here. 

[Patcon]

How many turns down are the mixture nuts?

Are you sure its rich?

Is the float fuel level correct?

[siteunseen]

I put a few gallons a year in my '72, it's 93 with 10% ethanol.

To be honest the most problems I've read on here is a result of low fuel chambers.

Get the floats right then you can adjust the carbs & timing correct. I tried and tried for a month then went to basics like my Dad taught me, now it's rock solid.

 

[DatsunZGuy]

Older cars without catalytic converters are not going to burn newer fuel as efficiently.  In fact, one of the main jobs of the catalytic converter is to change hydrogen sulfide into sulfur dioxide, which has no odor.

I just returned from a local cars and coffee event and pretty much every car older than 1980 smelled like it was running rich while driving past.  The bottom line is our Z cars will seem to run rich when compared to their newer contemporaries .  Better to run it bit rich than going too lean and risk engine damage.  IMHO

   

[Dadsun]

Thanks for the info on the float level. I will take a look. And also will have to refresh my memory on the mixture nuts turns. I'm pretty sure I wound up settling exactly halfway between all in and all out. I had bought and used the mixture tester that uses color.of the flame via spark plug port, but that seemed to work only once. Since then it shows a yellow flame no matter what I do. 

Back to the subject topic briefly: I have access near my house to both non ethanol 91 and 87 octane. Should I go with 87?

[w3wilkes]

I've used 91 non-ethanol and 88 non-ethanol. Can't tell the difference, they both run great. My altitude is pretty much 4,500 ft. and above.

Edited May 4 by w3wilkes

[SteveJ]

16 hours ago, Dadsun said:

Thanks for the info on the float level. I will take a look. And also will have to refresh my memory on the mixture nuts turns. I'm pretty sure I wound up settling exactly halfway between all in and all out. I had bought and used the mixture tester that uses color.of the flame via spark plug port, but that seemed to work only once. Since then it shows a yellow flame no matter what I do. 

Back to the subject topic briefly: I have access near my house to both non ethanol 91 and 87 octane. Should I go with 87?

Stock motor with stock compression - go with 87 or choose 91 if you like to burn money for no gain.

If you have higher compression, go with 91.

[Dadsun]

It is stock engine and good compression; was rebuilt about 15-20 years ago by original owner.  I will try the 87 for a few weeks and see how it goes.

[Yarb]

I need to find 93 octane ethanol free if someone knows a major distributor that offers that.

[SteveJ]

2 hours ago, Yarb said:

I need to find 93 octane ethanol free if someone knows a major distributor that offers that.

Dang, you must be running pretty good compression. You could try this website: https://www.sunocoracefuels.com/fuel-finder

There's a station near me that has a pump with 110 for "off-road use only". It's nice living not too far from a couple of tracks.

[Yarb]

Datsun Spirit stage 4 requires 93 octane. Not sure where I can find non-ethanol where I live.

[SteveJ]

42 minutes ago, Yarb said:

Datsun Spirit stage 4 requires 93 octane. Not sure where I can find non-ethanol where I live.

Try https://www.pure-gas.org/

[siteunseen]

On 5/4/2023 at 5:02 AM, SteveJ said:

Stock motor with stock compression - go with 87 or choose 91 if you like to burn money for no gain.

If you have higher compression, go with 91.

What's your thinking on cars that stay in the garage mostly? I know people reccomended adding octane boost for cars that sit for awhile between driving.

I've gone on the idea of more octane fuel added would kind of keep me on plane with additives without the exta effort but I learn something everytime I read classiczcars.com. 

[SteveJ]

6 minutes ago, siteunseen said:

What's your thinking on cars that stay in the garage mostly? I know people reccomended adding octane boost for cars that sit for awhile between driving.

I've gone on the idea of more octane fuel added would kind of keep me on plane with additives without the exta effort but I learn something everytime I read classiczcars.com. 

Octane boost fouls plugs. I had someone come over for a tune-up. I pulled a plug, and asked, "Do you run octane booster?" He was surprised I knew, but the plugs ratted him out.

Example:

Image shamelessly stolen from https://www.e90post.com/forums/showthread.php?t=1162289&page=2

Stabil is a fuel stabilizer and doesn't foul plugs AFAIK.

Edited May 6 by SteveJ

[siteunseen]

Well that's the reason I run high octane pump gas. My car sits for a month or so but when I finally have time for an early morning cruise through my close proximity "loop" I stop and add fresh 93 octane to perk the old gas up. So far so good but I do have a high end flutter.

Tomorrow morning I'm going to drive it and see if I can nail it down. Please stay tuned....I'll most likely need your help. 🥰

[Dadsun]

High end flutter? Hmmm. I seem to have that too.  I haven't checked the floats yet as someone mentioned at the start of the thread. And the flutter/sputter only happens when accelerating fairly aggressively in the 2800-3500 rpm range, it seems.  That rpm range while sitting still and just steady revving doesn't produce the flutter. Any ideas? I've got fresh gas. Right now it's a mix of 91 and 87 octane, all ethanol free. 

[Mark Maras]

@siteunseen, @Dadsun Have you tried easing the choke on during the flutter? Over the years I found the choke to be an easy method for checking lean mixtures.

[DC871F]

I just rebuilt my carbs, tuned and synced per the manual and it was very lean.

Turned mixture knobs almost a full turn RICH and it runs perfect.

 

[Dadsun]

How'd you determine it was running lean?

[DC871F]

4 minutes ago, Dadsun said:

How'd you determine it was running lean?

It wouldnt accelerate smoothly, surge during driving at any speed. I reached down and adjusted mixture controls and all problems solved.

Many years flying RC airplanes, they do exactly the same thing. The only thing I need to do is recheck the balance.