[RICK LAKE]

Tim 7139 Tim My timing for my fe is controlled by my FI system. The timing is locked out in the distributor. Timing controlled by ecu. Base is 10 degrees.
Heres the issues, Does the motor knock, ping, backfire out the intake or exhaust on coast down or hard hit to WOT? Do we have an A/F meter telling us A/F ratio out the tail pipe? What color are the spark plugs looking like? Are you adding a octane gas booster? When the motor is hot, does it start easy or a problem? If it doesn't have any drivibilities except for low mpg. Leave it alone.
If the camshaft is a 600" + lift monster in your motor and the motor only is pulling 10-13 hg you will need an adjustable vacuum advance with a soft setup. Yes a vacuum can will help stablize the signal. You may pickup 1-3 mpg. I don't have the size of your motor.
The other sensor I would have on the motor is a knock sensor and see where the motor is happy running and in a safe range, Reading of a knock sesnor would let you play with the timing without damage or pre ignition to the motor. Depending on where you live some placed change the fuel for different times of the year. We have 4 -5 different fuel changes in the NE area.
Here another thought, play in the timing chain. When new the chain is tight and no slack. With miles on them, they stretch and the timing starts to float. Gear to gear clearance between camshaft gear and distributor gear. this has effects on the timing.
If the motor is running a little soft and the MPG's are not bothering you, leave the motor alone. If you are looking for more power, better MPG, or little better drivability then switch. You can always swap back if this doesn't work out for you. Be careful with the ful timing at 36-38 total. More than this could be trouble. Rick L.