I've Checked All Over For This Engine, It's A New Gm Gen Vi Marine 502 415 Hp Pn 12568780. I'm Replacing An Old 330hp Gen Iv In A 1989 Scarab Excel 28. I Get Conflicting Information From The Supplier, Gm And Mercruiser, They All Point At Each Other And Give Me Base Timing From 4-10 Btdc An Max Timing From 26-36 Degress At 3600 Rpm Or 32 Degrees At 5000 Rpm. Does Anyone Know What It Should Be At Idle And Max Or Can Point Me In The Right Direction? Thanks

Mercs 500 EFI's are 8 degree base, for 36 total. I know that for a fact. If you run total of 34-36 you will be fine....

How you set the timing all depends on what ignition you are running.

Do you know what you have????? Is it the Merc off the 330???

Yes I was planning on using the old 330 hp thunderbolt distributor. Also running aluminum hi rise and 750 cfm carb.

I believe the 502 is 10 degrees and 32 @ 3000 rpm with the thunderbolt

If you are running the TB, it all depends on what module you are running. 34* total all in by at least 3000 RPM is where you want to be, so if you have a 20* module, you want 14* initial timing. You can't change what the module gives you, only the total/base.

Set the max timing where you want it. Do this at about 4000 rpm or whatever RPM the timing stops advancing. If you use 4500 RPM you are sure to be there. Set it @ 32 Deg to be safe an extra two degrees will buy you nothing and this setting will protect you if you run into some bad fuel. The initial timing will lay wherever it does, you cannot change that with these modules. The only thing you can do is check that the timing is advancing as you rev the engine, if it does, the module is working. Set the max and forget the rest. Check it again after you lock it down.

Get the numbers off the ignition module that you have. That will determine where to set base timing. After that, you can fine tune the full advance. Different modules have different curves and depending on which one you have will dictate what rpm you need to check full advance timing. Some will go to full advance at 3000rpms while others are at 5000rpms.