I need to re jet my nikki for a semi bridge. It's running 15:1 on idle aeround 2k rpm and maybe a little lean on power. Will the mazdatrix jets work in the slow speed position. If so how big should I go compared to the stock ones.

 

As I had a spare Nikki to play with, I just drilled jets until I was happy with the AFR.
I machined the primaries ventury to 24mm, and so far my stockport is happy with 110 on the primary fuel jets (from 92).
I dod not touch the idel jets, but I had to play with idle speed screw and richness screw.

We'll see when the halfbridge is closed and in the car again.

 

You need to go as large as you can but at some point you will need to modify the air bleeds. When I did my hogged out nikki I was able to get the nikki tuned without going that far but it was a stock port 12A. @jeff13b would have more knowledge about nikki jetting for various porting.

 

Have modified Venturis if interested. These are stock size worked good for my street port 13b. Can go bigger if u want. $20 plus shipping.

 

not to speak out of turn, but do you mean @Jeff20B ?

 

You will have to ignore the wideband at idle and cruise because the misfiring will add a bunch of air to the exhaust, making the sensor read lean.

From practical experience, there is no way it could be idling at a genuine 15:1

Give it what makes it happy and ignore the numbers, especially at low load and idle when it is stuttering. That isn't to say that the gauge won't be useful, but the numbers will only make sense when the engine is loaded enough to run cleanly.

 

yes oops.

 

It's quite possible you have an exhaust leak introducing air into your exhaust at idle that then reads correctly with more RPM. I had the exact same issue with a WRX I used to have. Thing would read full lean at idle then show normal readings when actually driving. There no way it's idling at 15:1, mine idles happy at about 11.5-12.5:1.

I'm on a stock port 12a with bored primary venturis and mech secondaries and my car seems to be the happiest at pic attached, the last number would be the current. It seems like to me that Nikki tuning is super temperamental and not consistent between cars at all. I have to run mine at around 12:1 at all rpms to avoid most of the secondary bog. Compared to others that get away with much smaller jets. Either that or I'm doing something wildly wrong which is also possible. Basically you are probably gonna have to get a good handful of jets and play around with it.