502 Timing
 

I have seen a lot of talk back and forth on timing for full advance, also saw this in Dennis Moores book. But why does Merc put such a small advance box on the older 502 mags with carbs?? What should be the full advanced timing? If you bump the timing say to 12 initial do you need to run premium fuel?

My thoughts on this is,
back when these engines/ drives
came out, they would only offer them
with 1:36 gear ratio's to prevent
drive issues.
Retarded timing= less low end torque,
easier on the drive, when coming out of the
hole.

As I recall the module only has 20* of advance
built in, that gives you a total of 28* full,

I had a 24' boat with the engine mentioned,
it was relatively light 3600#'s, but it was a pig
out of the hole
I set my advance up to 14* initial, giving my
34* total, made a big difference on acceleration.
I didn't run premium either, I didn't notice any
detonation, I ran this for 5 years,no problem.

hope this helps.
jt

502
 

I had not thought of it that way. Although I have 1:50 drives. My hole shot is pretty good actually and the boat stays on plane at low RPM. I have bumped my timing a little (last season), but was starting to think about the upcoming season and stuff to put on my to do list. It seems to me that there is more power available there with some better tuning. I appreciate your feedback. Any other input out there? Thanks!!

Your module should have the amount of advance stamped into the case as part of the part#. It is probably a 24* degree advance. Whatever it is, set the timing to 34* at full advance. This will come in at 3000-3800 depending on which module you have. Factory setting is 32*.