1985 Mercruiser 120 Timing

[zbadboy]

I have searched and found different answers in reference to timing for the Merc 120. Allot of people are setting it at 6* BTDC. However the mercuiser Manual states 8* BTDC on the 120 and 6* BTDC for the Merc 140.

The dwell range in the Mercruiser manual states 28* - 34* for both. I just replaced the points and have mine set at 30* on the dwell meter. Is this a good spot for the dwell? My timing is at about 4*. I only have an old school timing light.

The boat is idling at 750 in the driveway on muffs. I know the manual says 8* and is probably where I should be at, however just wanted some clarification. Also does the boat have to be in gear? Thanks

 

[Don S]

Re: 1985 Mercruiser 120 Timing

Here are the specs for the 85 120 from OEM manual #10 for 85 thru 89 120's and 140's using the Delco distributor.
All I see is 8? for the 120. 6? is for the 140.

 

[zbadboy]

Re: 1985 Mercruiser 120 Timing

Thanks Don S. I went ahead and went with 8*. The dwell is at about 30*. The range is 28-34* according to the manual. Is there a preferred setting High low middle or does it not really matter? Thanks for your quick response.

 

[Aloysius]

Re: 1985 Mercruiser 120 Timing

Dwell is not real important. If it's too high, the points will "burn". too low, the spark can be weak at high rpms.

Dwell is the angle during which the points are closed.

Timing should be set AFTER dwell is adjusted, as the dwell affects the initial timing.

 

[zbadboy]

Re: 1985 Mercruiser 120 Timing

Is it worth messing with it to get it to 31* ? It's just shy of 30* on the needle.

 

[Aloysius]

Re: 1985 Mercruiser 120 Timing

Absolutely not.

 

[zbadboy]

Re: 1985 Mercruiser 120 Timing

Thanks I am going to try to get it out this week.