This is my first Harley.. and first V-Twin. I am not sure what to run in the Primary. I am using Castrol 20-50 RS V-Twin Synthetic for engine. What will be the best choice for Primary ?

Thanks in advance.

 

 

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So I changed out the Primary Oil. It looked very clean and the magnet has practically nothing on it. I used Mobil 75-90. After letting it warm up I took it for a 1 mile spin. Returned home and at idle I can hear noise coming form the primary that I have never heard before. Not sure what to think of it. I checked the fluid level and its correct. Kind of concerned to even ride it..