dist. mechanical advance ajustment?

j.d.duggan said
pretty much stock 340,bought new spectra premium dist.trying to get some fuel mileage out of this thing and think vac. advance will help.I have msd box,if it maters.my engine likes to start and idle at 10* btdc.

if there had been a nonsmog 340 in 68 it probably would have had initial timing around 10* 600rpm

j.d.duggan said
The dist. I have is a ch04,spectra #.the problem is,it has 30* of mechanical advance in it.trying to keep my total to 34*,I have to set my initial at 4*,does not like this for starting

usually less timing makes for easier starting but doesnt idle as well at low rpm.

j.d.duggan said
my vac. can on this dist. has 22* in it.I think if I could set my total mech. adv.to 24*,then set my initial to 10*,I should have 34 total and 56 cruising.

it depends on what the cruise vacuum is and the mechanical timing at highway cruise. Mecahnical advance should not be all in until at least 3000 rpm.

Vacuum advance: How To Limit and Adjust Chrysler Vacuum Advance Cans Go to the very last picture for MP instruction sheet.

Reducing the allowable advance: Tack a weld the inside of the slots. result will be like discussed here: Erratic Timing
Doing the outside makes it much more difficult to work with vac advance and getting the high rpm slope that helps at the top end.

Changing the adv start rpm, and how many degrees out the second spring joins in is here: Erratic Timing