Idle Mixture Problem Solved

 I did some reading of the Stromberg NA-S3 manual and on-line.  Bob Kachergius, "The Stromberg Specialist", has a good article on how to adjust the idle mixture.  There is a needle valve with an adjustment screw on the back of the carburetor.

Rather than have a mechanical accelerator pump, this carburetor has 2 Idle Discharge Nozzles.  One nozzle is above the Throttle Valve, when the valve is closed at idle.  As long as the valve is closed it provides all the fuel needed to keep the motor running.  

As soon as you open the Throttle Valve a little, the second port is uncovered to allow some extra fuel until the motor speed increases to about 1000 RPM.  

Above 1000 RPM the Main Metering Jet provides the needed fuel, if the float is properly adjusted.

If the Idle nozzles are adjusted too lean the motor will stumble or stall while opening the throttle, my problem exactly.  

Bob's procedure has you install the Idle Adjustment Needle Valve without the spring so you can accurately count the number of turns until the needle gently seats.  He says it should be 6 1/2 to 7 turns.  I have another carb. which does need 7 turns.  The needle on the Fly Baby carb. only went in 4 1/2 turns, don't over tighten.  His recommendation is for an initial opening, with the spring installed, of 3 turns.  Then you open the valve in 1/4 turn increments, if needed to solve the idle problem.  I started with 2 turns and it runs great.  No hesitation nor missing.

By the time I was done it was a 4 o'clock and the sun was right in my eyes heading down runway 23.  I decided to go back tomorrow so I can fly earlier in the afternoon.  Hopefully it will be as nice as today.