If you think it really has something to do with vacuum advance see if it moves properly (be careful not to bend anything) inside the distributor. Sometimes those bearings get rusty. Most times on these machines i have found something affecting the balance hose hooked up to the back of the vaporizer. Unhook the hose hooked up to the bottom of the back plate of the vaporizer and see if power increases. Check timing setting as well. ron_k is also correct about all his points. if timing advance makes it go up a ramp don't worry about the inching cable right now. About intake crud? I once had one of these intakes carboned up to the point of having 3/4 of the airflow gone.