timing question 4.3 liter v6 1987

The former owner of my boat had the timing retarded 2 degrees so it could burn regular gas, 87 octane, without spark knock. I have switched to 90 octane rec fuel. Should the timing be restored to 0 ?

if you are using the recommended fuel, then use the factory timing spec...and make sure the timing advance works ...

the spec on those is 6*BTDC, using 89 or above AKT fuel. I use that when using 89 octane gas (gas station) the gas docks here sell only 93 octane.
those Prestolite distributors have mechanical advance IIRC they are spec'd to give 12* advance at 3200 rpm for a total of 18*.
in the OMC owners manual it says to set it at 1*BTDC if using 86 AKI fuel (low grade regular) and 6*BTDC if using 89 AKI fuel (mid range gas). Here our low grade regular is 87, but in some high altitude regions it is 86 or even 85.
Marine inboards are highly loaded all the time, I always err on the side of caution with fuel octane, no point saving money to risk detonation.

In fact yesterday I was on our boat & on the flame arrestor it says to use 89 octane fuel if not then you’re supposed to retard the timing.

Found the original owners operators manual! 1987 4.3 v6 Calls for 90 RON ( 90 octane fuel ), timing to be set to 1 degree BTDC. Have a source of 90 octane rec fuel now that may help performance overall with the 4.3 engine. Thanks for all your replies. Great forum.

BTW if you’re in the US & Canada gas is sold by the AKI formula and the minimum recommended by OMC was 89 if using 89 AKI fuel then you can advance the timing to 6*BTDC for better performance. If using lower octane than that then the spec calls for retarding it to 1*BTDC. I’ve always used at a minimum 89 octane but our gas docks only sell 93. In older marine engines that don’t have a knock sensor you want to avoid pinging & detonation from low octane fuel because they don’t have knock sensors to automatically retard the timing if knocking happens due to low octane fuel.
So spend a little more & preserve your engine & get better performance at the same time. Retarded timing severely handicaps performance so use the fuel needed to set it at normal specs. It’s likely that OMC made this recommendation because unlike automotive engines marine engines are under constant load.