I am finding that I get the best overall idle quality (highest vacuum, smoothest) with initial advance over 30* BTDC. This is with a hot engine, and it has no difficulty starting with such extreme advance. I PROMISE I verified that the TDC mark on the damper is accurate within a couple of degrees. Dwell is 38*, idle speed 650 in park, mixture screw 2 turns from seated.
Some months ago I tried driving the car at that setting without altering the curve at all. I got some spark knock under load so I backed it off until I was at 20* initial, and that is where it has been ever since.
How can my engine actually prefer so much advance?
I was wondering, if there is a whole lot of slop in the timing chain, could it be that the valve timing is late enough that I'm retaining some exhaust gases in the cylinder and they are slowing the burn rate to the point where the extra advance helps? 98k miles on the engine and I don't believe it's ever been rebuilt.
Some months ago I tried driving the car at that setting without altering the curve at all. I got some spark knock under load so I backed it off until I was at 20* initial, and that is where it has been ever since.
How can my engine actually prefer so much advance?
I was wondering, if there is a whole lot of slop in the timing chain, could it be that the valve timing is late enough that I'm retaining some exhaust gases in the cylinder and they are slowing the burn rate to the point where the extra advance helps? 98k miles on the engine and I don't believe it's ever been rebuilt.