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

[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, 2023 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?