Need basic tuning help (setting initial timing)
How do you set initial timing on a carb/distributor engine? Do you use a vacuum gauge and adjust it until you get the best vacuum reading?
I just reassembled a mild 351C (9.0:1 CR) with a healthier than stock cam (0.529/0.540", 220/226 @ 0.050"). I am running a low-rise Weiand single plane intake with a 600 CFM Edelbrock Performer carb (might be a bit too small now).
After playing with a vacuum gauge, it would appear that the car wants almost 20º initial timing to idle with decent vacuum (16-17"). If I set timing around 10-12º, vacuum is 7-10" and actually increases once I crack the throttle and increase engine speed. I fast idled the engine during cam break-in and got around 17" vacuum at 3,000rpm.
I've checked for vacuum leaks and as a result disconnected the power brake booster until I can replace it. Other than that, I found no leaks. The cam called for a 108º intake centerline. With my timing set, the closest I could get was 110.5º. Cylinder/ring seal is solid.
What do you guys think?
1973 Cougar XR-7 convertible - 351C, 9:1 CR, 2V heads, Crower Ultra Beast, Weiand X–CELerator, 600CFM Edelbrock Performer, Dynamax long tubes, stock FMX, 3.89s w/ Detroit Locker