My experience with tuning the Hitachi SU carb setup on my Datsun 240Z is a hobby passion spanning some time. I have tuned the L28 stroker motor in my 240Z for over a decade with a variety of configurations. One of my most favourite fuel delivery to date is the factory Hitachi SU carbs. In my pursuit for the optimised tune I have learned a few things and found some really good tuning tools. Welcome to my three must have tools for tuning Hitachi SU carbs!
You should already have a uni-syn on deck as part of your ordinary Hitachi SU carb tuning kit. Why get another air flow measuring device? Well this synchometer is designed for use with side draught carbs (eg. DCOE Webers) and inherently measures smaller air flows more accurately.
The Uni-Syn has an adjustable orifice. The synchometer is a fixed unit calibrated and much better suited to measuring airflow at idle and lower RPM. It might seem unnecessary. For me having a balanced idle is important as it affects many behavioural aspects of your motor.
2. Innovate WBO2 datalogger
If ever you wanted to verify your carb tune against a variety of parameters, the Innovate LM-2 is the kit you need.
I purchased my kit back in 2009 and have been using it at a hobby level since. You will have to locate and weld in an bung for the sensor if not already provided in your exhaust system. The unit does use a dated SD card system to log data if you do not log directly to your computer.
One benefit of this system as it allows for a variety of analogous inputs that can be configured through the Logworks software. So yes, you could log your carb’s tune against RPM, TPS and MAP if you equip the sensors. How good it that!?
1. Float Sync
This is the one tool you must have in your Hitachi SU carb tuning kit. PERIOD!
What this tool allows you to do is visually assessment the fuel float height. I found I was able to make precise adjustments and calibrate front and rear carbs to be synchronised. Out of sync fuel levels between the front and rear carbs can make you chase your tail when tuning.
When I was making needle adjustments I used the Float-Sync to raise and lower the fuel levels to change the station on the needles. What good is this? Well I was able to determine and narrow down my needle selection by observing the change in AFR from an estimated need station through my LM-2.
If you are keen about tuning your own hitachi SU carbs, consider purchasing these three tools. I used to fumble my way through a tuning with a ‘she’ll be right’ result. After I used these tools I started to see better power production and fuel economy. With further investigation I suspect I could optimise the tune even more. There are setups out there netting over 230wrhp on L6 motors!
Thanks for reading guys. Catch ya in the next one!
L28 Stroker build information: https://builtonpurpose.co/diy-guides/l28-stroker/
Datsun Z car ignition upgrade guide: https://builtonpurpose.co/diy-guides/ignition-upgrade-guide/
My YouTube channel: https://www.youtube.com/builtonpurpose