One of my favorite tools here at Datsun Ranch… This solution saves a ton of time on tuning an old Datsun!
Setting float levels in your Datsun SU carburetors is critical to optimal engine performance. Power and fuel economy are sacrificed if float levels are set too high, too low, or differ in each bowl. Until now, there hasn’t been a tool allowing you to visually inspect both float levels at the same time, with the engine running. Float-Sync shows you precisely where your floats are set to ensure your engine is running with peak power and efficiency. 
The level of fuel in the float bowl dictates the level of fuel in the jet nozzle. This is a big deal for SU carburetors because the fuel level in the jet nozzle directly impacts engine performance. When the engine is running, a vacuum is created in the SU carburetor venturi that pulls fuel out of the jet nozzle, mixing it with air and drawing it into the engine. If float levels are adjusted too high, fuel puddles at the top of the jet, allowing too much to be drawn into the engine, creating a rich condition. If the float is adjusted too low, it will be harder to pull fuel out of the jet, creating a lean condition.
A rich condition can cause plug fouling, poor fuel economy, gas fumes, diluted crankcase oil (contributing to blow by and reduced engine protection), and in extreme cases potential for an engine fire. A lean condition can cause the engine to stumble, backfire, ping and run hotter than it should, creating the potential to burn the valves.
Only Float-Sync allows you to see precisely where your floats are, and shows you the fuel level throughout the entire RPM range in each float bowl… all without opening the float bowl.
Setting floats by removing the float bowl lid and measuring the distance between the lid and top of the float is imprecise at best, because there are so many other variables.
To make float adjustments, remove the four screws on each float bowl and lift the cover off with float attached. The metal tabs on the floats can be bent slightly up or down to change the fuel level in each bowl. With the float hanging below the cover, bending the float tab down will raise the fuel level in the bowl. Bending the tab up on the float will lower the fuel level. To observe how your adjustments have changed fuel level in the bowls, replace and secure covers, then restart the car to inspect fuel levels. Be patient, it may take a few attempts to sync float levels precisely.
Float-Sync Directions:
- Remove and set aside the air cleaner housing and filter.
- Remove 12mm threaded plugs on the front of each float bowl, taking care to collect the gasoline which will drain.
- Screw Float-Sync tools into each opening so sight glasses point up and neoprene washers compress slightly so they seal against fuel leaks.
- Start car and allow engine to warm up. View fuel level through each sight glass. You want the fuel level in each sight glass to be the same. The optimal level is 9/16” (14mm), measured from the top of the Float-Sync block to the fuel level in each site glass.
- If adjustments are necessary, disconnect the fuel hoses supplying each carburetor, remove the four screws on each float bowl lid and lift cover off, with floats attached. Metal tabs on floats can be bent slightly up or down to change the fuel level in each bowl. When the float is hanging below the cover, bending the tab down raises the fuel level. Bending the tab up lowers the fuel level.
- To observe how your adjustments have impacted the fuel level, replace and secure float bowl covers, reattach fuel hoses and restart car. Be patient, it may take a few attempts to sync float levels precisely.
- With both floats adjusted properly, remove Float-Sync units, replacing them with the 12mm threaded plugs you removed. Again, take care to collect gasoline which will drain from float bowls. Replace air cleaner and filter.
You can buy Float-Sync here! Float-Sync Tuning Tool for Datsun SU Carburetors