[tdangle]

You have a carb issue. Don't worry about the timing right now, Factory settings were anywhere between 0 and 6 degrees BTDC and they idled just fine. A small vacuum leak will raise the idle slightly but not to 1700 RPM. A large vac leak will cause the engine to stall normally.

I suspect the float got stuck while you had the carb off and you may have fuel drizzling from the primary boosters. This happened to me once. The reason the RPM drops when you force the throttle closed even more is that fully closed they have a very slight gap in the bore.

Your original idle problem may very well have been a vac leak or mis-adjusted carb. Increasing the initial timing only helps throttle response and will with all things equal will slightly increase idle speed

I was always taught KISS (keep it simple stupid)