1975 RD350 - Right Cylinder Not Firing - Issue Follows Carb

[KONOW]

I recently acquired a non-running 1975 RD350 that hadn't been started in three years. The previous owner noted weak spark as the reason it was not running well and believed it needed a new ignition system. I received the bike mostly assembled except for the rotor and ignition system, which I installed and set the timing to 1.8mm before top dead center. I confirmed strong spark on both cylinders and got the bike to fire up, but it's only running on the left cylinder at idle. Right cylinder is dead at idle.



Initial Troubleshooting:

1. Confirmed strong spark present on both cylinders

2. When I cover the right carb inlet (with the air boot removed), I can draw fuel in manually, the right cylinder fires and maintains idle. Once I remove my hand and normal airflow resumes, the cylinder goes dead.

3. Swapped the left and right carburetors

    3.1 With the left carb installed on the right side, the right cylinder fires normally

    3.2 With the original right carb installed on the left side, the left cylinder does not fire

4. Swapped the throttle slides between the two carb bodies (keeping each carb body in its original location on the bike)

    4.1 With the left throttle slide installed in the right carb body, the right cylinder came alive

    4.2 With the right throttle slide installed in the left carb body, the left cylinder went dead

    4.3 I understand that these slides are asymmetric and this test might not prove that the issue follows the slide. With the slides installed on the incorrect carbs the fuel/air circuitry is likely not acting as intended.

5. Swapped the threaded throttle slide caps between carburetors — no effect

6. Swapped jet needles between carburetors — no effect

7. I have cleaned both carbs but I have not drilled/removed the brass ball on either carbs



Carburetor Observations:

1. The left carb (with choke lever) has a float bowl with an orifice jet

2. The right carb (no choke lever) has a float bowl without an orifice jet

3. The right carb has a hollow brass tube attached to the carb body positioned near the pilot jet; I cannot pass music wire through it or blow air through it to determine how it relates to the carb circuit (photos attached)

    3.1 This is confusing because I would expect this brass tube to be present on the left carb w/ choke, not the right carb. To be clear the left carb does not have this brass tube.

4. Air screws on both carbs are set to 1.75 turns out

5. Float height on the right carb (the non-firing side) measures 15.5mm



My questions are:



1. What is the purpose of the hollow brass tube on the right side carb body and if it is functional which circuit is it connected to?

2. Are my float bowls installed in the correct location?

3. What additional troubleshooting steps can I perform to identify the issue?

4. Is it likely I need to drill out the brass ball and clean that portion of the circuit?

5. For the choke lever which position is on/off?
   

Thanks!