Performance timing

MaxTax : i went out today got the motor fully warmed up and vaccum advance still plugged off and at idle in park i turned the distributor till the timing on the tape read 15º on the 0 mark on timing cover and idle is at 800 rpm . When i hook up the vaccum advance i can hear the rpm's come up and the timing reads 42º at the 0 mark on the timing cover and rpm is at 1000. Where do i go from here?