Need help with su tuning

[Mochi]

I need help with dialing in the last bit of the carbs. At idle I am running around 10ish afr. At part throttle acceleration am 15ish afr. At WOT I am 14 flat. At cruising in 4 gear around 55 mph I am 14ish. What gives on the idle? The needles look like there are no ware marks. I have synced the carbs, aligned the jets(pain in the butt), and set idle around 800ish. The spark plugs have been running rich but have finally got a good ish tune.

[nismou20]

Have you tried running oem NGK or Denso? Wonder if maybe the stock oem Ignition may not be up to snuff to work the contemporary plugs such as Iridium efficiently. Are the plugs copper core?

[GeoffM]

From my own experience and the anecdotes on the forums, 1600's are known to run rich at idle. Based on your AFR numbers, you've got it pretty dialed in. I use Keith Olan's carb set-up guide on the wiki, which results in focusing the carb set-up on the 2000-3000rpm range (where ever you set the high speed idle rpm during your tuning). From a performance standpoint the mid-rpm AFR is the most important if it's a street car.

Edit: Forgot to mention that you can raise the needles up a bit to lean out idle (raise the shoulder so it sits proud of the piston face) but this also affects the rest of the mixture curve.

[Bwk2000]

With my 1600, I can get the car running very smooth at idle or at 2000 rpm … not both.
+1 on Geoff’s recommendation - Follow the Keith Williams write up and dial in the carbs at 2000 rpm. You get a little loping at idle but the rest of the operating range is great (and plugs still look good after a long run).

I use to have them set up for smooth idle (~650 rpm) but got tired of bouncing back and forth between lean and rich driving issues under load/acceleration all the time.

[Mochi]

Have you tried running oem NGK or Denso? Wonder if maybe the stock oem Ignition may not be up to snuff to work the contemporary plugs such as Iridium efficiently. Are the plugs copper core?

I was thinking with electronic ignition I should use a more modern plug. After multiple long runs and I can confirm my tune. I will try some basic copper.


Oh I forgot I am running 89 pump gas. I don't think running higher would help?

[Gregs672000]

I do know that some ignition systems are particular, and work best with certain plugs (my Ford EDIS needs a double platinum design due to being a "wasted spark" ignition). Your options to tune out the areas you mention are extremely limited by the carburetor design. About all you could do would be to try different needles to see what happens overall. I do wonder if you could richen up your "part throttle acceleration" into the 13-14 range with a heavier dash pot oil, as doesn't that help control the carb piston speed and thus richen the mix for a bit? Since you have a wideband it seems, could be fun and informative to experiment. You might check your ignition timing and play with that a few degrees either way and see what your idle mix does.

[Gregs672000]

It will idle best with out loading up at around a 13.2 or so.

[keith0alan]

The Nissan needles all tend to run rich at idle. I recommend the ADQ needles. Also you can set the needle out a few thousandths of an inch. This has a big effect at idle and almost none at mid range and top end.

[redroadster]

This is why it's supposed to be done with a gas anylizer
Machine
And irridium / platinum plugs really only designed for fuel injected cars they foul easily , no very easily
You can carbon up the ring lands then scratch up cyls
Way rich
Assuming the plugs are low miles that looks very rich
One of mine slide were worn and the slide held up not bottoming out fully intermittently

[spl310]

Keith, what needles do you recommend for a 2000? Does it matter which cam?

[Mochi]

I do know that some ignition systems are particular, and work best with certain plugs (my Ford EDIS needs a double platinum design due to being a "wasted spark" ignition). Your options to tune out the areas you mention are extremely limited by the carburetor design. About all you could do would be to try different needles to see what happens overall. I do wonder if you could richen up your "part throttle acceleration" into the 13-14 range with a heavier dash pot oil, as doesn't that help control the carb piston speed and thus richen the mix for a bit? Since you have a wideband it seems, could be fun and informative to experiment. You might check your ignition timing and play with that a few degrees either way and see what your idle mix does.

Hehe you are telepathic! I just got 30 weight oil to put in to try and slow the piston down a little. I have advanced the timing too with those numbers. Advancing the timing has improved idle a little and overall drivability by alot.

[Mochi]

The Nissan needles all tend to run rich at idle. I recommend the ADQ needles. Also you can set the needle out a few thousandths of an inch. This has a big effect at idle and almost none at mid range and top end.

I did see a couple of posts about the adq needles. They seem kinda hard to find. Keith would you happen to have some laying around? I might have to post up in the classifieds want for some

[nismou20]

For a U20 I’m a fan of RA needles!

[Gregs672000]

Glad that helped. It's pretty important that the timing is working as it should, both for power and engine safety. If you have a dial back timing light you can get your max timing (should be all in by 3800 rpm, maybe earlier). That should be around 34-36 degrees without a high load, and the vac advance should pull out 3-4 degrees or so I think when the engine is under load. IMHO you should use a standard NGK BR6ES plug. I'm having a hard time reading your plugs. They look lean on the insulator and rich on the parameter. Do you have a wideband? If you do, and the carbs are in good shape, it would probably be helpful to many to get an idea of what can be done to change ratios, and/or if some needles seem to work better than others as has been suggested. Or document different dash pot oil weight and effects. Might be fun, if you're so inclined!

[keith0alan]

Yes, I stock ADQ needles. They were not fit to cars imported to this country so they tend to be hard to find here. I import them from England. The RA needle seems to be what folks are using since the N-17 needles from Nissan went away.