It doesn't really smoke in a normal scenario. It does smoke some on acceleration. I had the head done 40 years ago but the machinist didn't replace the guides. He reamed them to save me money. So it's possible that guide is sloppy now. Plus the valve seals are 40 yo now...

I like the pretty new head Astrohog has. I might just do that sooner then later and then build a block to go under it

@inline6

Garrett what did you ever do to resolve your air filter not being thick enough. I don't recall the solution and I have the same problem...

So I need to change the dash pot oil. On acceleration it's too lean 14.7 - 15.1.

So they currently have transmission fluid in them. What would the next step up be?

@Captain Obvious

Chat gpt is pretty good. I am getting hooked on it.

https://chatgpt.com/s/t_6a0a437b9b608191ad3f471c8cb51968

Oil Type	Approx. Viscosity	Effect on Throttle Response	Best Use
Sewing machine oil / 3-in-1	Very light (~5W)	Fast piston rise, leaner tip-in	Warm climates, highly modified engines
ATF / Marvel Mystery Oil	Light (~7.5W–10W)	Crisp response	Close to factory feel
10W engine oil	Medium-light	Good balance	Factory spec for many Datsuns
20W oil / 20W fork oil	Medium	Richer acceleration	Mild hesitation or flat spot
30W oil	Medium-heavy	Slower piston rise, richer tip-in	Hot weather, stock engines
20W-50	Heavy	Strong enrichment	Worn engines or persistent stumble
No oil	None	Very lean/quick	Race-only experimentation

Edited May 17May 17 by emccallum

That's pretty cool. My wife uses AI all the time. I'm not there yet, but those results are impressive!

I'm not sure I have any 10W. I might have some fork oil...

Are you guys really looking at and absorbing the AI "stuff".

If 7.5W - 10W is light how can 10W be medium-light?

What does "good balance" even mean? (Nothing).

Richer tip-in? Has no meaning. Richer acceleration? Feels like it has meaning but when you really think about it it doesn't.

Are the recommendations to fix a "best use" or to avoid it? "Close to factory feel" and "hot weather" and "flat spot" are all under Best Use.

The AI's are designed to make the users feel good. Like a drug. Apparently an addictive drug, Don't overdo them!

Check out the Sources. They're the usual suspects. The AI just blends them all together and excretes something that looks authoritative.

Edited May 18May 18 by Zed Head

Well, I don't know about the whole thing, but I know what "tip in" is...

If you have 10W-30 laying around, I'd try that.

Are you double dog sure you got all your vacuum leaks sealed up now?

Oh, and a couple other details about the carbs... Are you running stock needles? Stock springs?

Sorry for the rant. I worry about being surrounded by people on their phones asking them what to think.

Here's an example of how detailed experience gets distilled down to something by "AI". You can see the pieces that remain, like unchewed kernels of corn or chewed gum, in the AI response.

This guy Keith Williams seems well known in Datsun world. Why not just read his original material? It seems more informative than what the "super-brain" produced.

Anyway, it looks like experimentation is required. Good luck.

https://www.311s.org/su-setup/su-setup.html

Dashpot Oil

 

On acceleration the mixture needs to be richer or you will get stumbling. The oil in the dash pot slows the rise of the piston. The piston being lower than it wants to be causes the mixture to be rich. Generally speaking you want to use the thinnest oil that stops stumbling on acceleration. Roadsters tend to be quite tolerant of running rich so thicker is better than thinner. However, too thick will over richen and cause the acceleration to feel flat. The correct thickness will have a crisp acceleration. The factory spec is 10w. That is in the range of ATF and MMO. 3 in 1 is thinner. In one Z I did I ended up with 50w before it would accelerate cleanly. The synthetic oils do tend to be thinner than regular oils so I'm not sure what the "real" viscosity of the synthetic is. Motorcycle fork oil works well, comes in convenient bottles, and in lots of weights. Single weight engine oil comes in 20, 30, 40, and 50 weight but I haven't seen 10w. If you're being fiddly you can mix weights to come up with in between weights. I use fork oil for the thinner weights and single weight engine for the thicker.