If you had not bypassed the oil injection I might suspect that as the issue. 97 600 twins had huge issues with oil pumps failing. When those fail they fail full flow. Mine went on my 97, and was probably bad for years. I bought the sled only last year and knew once I started reading about the oil pump issues that this was a problem. It explained my plug fouling and stinky idling sled. After getting the new oil pump, it really woke the sled up.
I bet there is a way to test the solenoids on the smart carbs to determine if those are the issue.
I am assuming the carbs have been cleaned recently, right?