Tuning carbs is simple albeit time consuming once you understand the basic subsystems found in all carbs.

Assuming timing advance systems are working correctly, your problem can be a too lean main jet or more likely something to do with the power system. If the carb has a vacuum secondary, that could be your problem, but most 650 hollers have mechanical secondaries.

There is a book, published by HP Books, that has been in print for over 40 years. I think it is called Holley Carburetors. It is an EXCELLENT book for learning the principles of carburetion, and the specifics of Holleys. Regardless of what carb you are messing with, this book will teach you the principles that you need to understand.

The subsystems in a carb interact, so if you don't understand the principles, you will be chasing your tail.

Hope this helps.