merc 225S timing

[rebars1]

1974 merc 225S, Ford 302. The Merc manual lists the timing for 10 degrees BTDC. But it also has a footnote to retard it 4 degrees if using unleaded gasoline.

Does that mean it should be set at 6 degrees BTDC? (sorry if it sounds like an obvious answer). Why would unleaded fuel make a difference?

Also, when setting the timing, should it be done with the engine running or off? I have a timing light.

Thank You

 

[Bondo]

Re: merc 225S timing

Hi Rebars,.....

The Timing is set at Idle with the sensor attached to the #1 wire......

And,......
I'd run it at 6*s if that's what it calls for.....

Lead has a lubricating,+ stabilizing effect to the fuel,+ 10* might be Too Hot for it when running Unleaded fuel.....

 

[rebars1]

Re: merc 225S timing

Thanks Bondo.

Are the scribe marks on the harmonic balancer in one-degree increments or two-degree increments?

 

[Reel Poor]

Re: merc 225S timing

They should be in 2 degree increments.

 

[rebars1]

Re: merc 225S timing

I re-read the note in the Merc manual and it reads to retard 4 degrees if using unleaded gasoline with octane rating between 86 and 88.

Around here we have 87, 89, or 90 octanes, so, the original 10 degrees would apply unless I can't get the higher octane (89) rated fuel.

 

[Reel Poor]

Re: merc 225S timing

If you want to afford the premium 90+ octane fuel you should be good @ 7 to 8 degrees, 6 degrees would be the prefered setting with any other octane fuels. This should put you in a safe operating range. The unleaded fuels burn a little hotter than the leaded fuels of the past. Aftermarkert lead additives are also avaliable if you wanted to use the factory 10 degrees, you will just have to add the lead additive each time you fuel the boat.