detailed instructions on setting 1974 merc 850 timing

[rcb130]

I am working on a 1974 Merc 850, Serial No. 3877808. Can anyone give me detailed instructions on how to advance or retard the timing on this motor? I see all kinds of posts on this forum pertaining to adjusting the timing but nothing that is clearly stated other than "adjust the timing for 4-6 btc". How exactly does one do this? I have a merc manual but it is fuzzy in this area also and the pictures suck.
Thanks

 

[Chris1956]

Re: detailed instructions on setting 1974 merc 850 timing

That motor has a distributor right? About 1/2 way up the distributor is a brass collar. This collar has plastic coated tips that open the carbs, as the distributor rotates. Follow the length of the collar, and you will see two 5/16" stainless bolts. These may be loosened to move the collar and change the idle pickup timing. The idle pickup timing needs to be 4-6* BTDC.

Remove all spark plugs but #1 spark plug. Install the other spark plugs into their wires and tape them together and ground their bases to the block. Remove the prop. Install a timing light on #1 spark plug. Turn the ign on and put motor in gear. Crank the motor by jumpering the starter soleoid and set the throttle to 4-6* BTDC. Now loosen the two 5/16" bolts and rotate the collar until the carbs are closed but just ready to open. Tighten the bolts.

Set the throttle to full and crank motor. Turn max spark advance set screw until you get a 21* BTDC advance. Tighten the set screw.

 

[JB]

Re: detailed instructions on setting 1974 merc 850 timing

Have you considered a Service Manual, rcb??

 

[rcb130]

Re: detailed instructions on setting 1974 merc 850 timing

Chris,
Thanks so much for the info, greatly appreciated.
rcb130

 

[rcb130]

Re: detailed instructions on setting 1974 merc 850 timing

Most Ancient Mariner,
As I stated in my original post, I do have a service manual but it leaves something to be desired.
I learned long ago to get service manuals for outboard motors. I don't mean to sound like a smart $#%, but I did post that I had a manual.

 

[Fed]

Re: detailed instructions on setting 1974 merc 850 timing

Is it a genuine mercury manual?
I've found then detailed to the point of making me feel like they think we're all idiots.

 

[JB]

Re: detailed instructions on setting 1974 merc 850 timing

Yes, you did, rcb. And it was so lost in a neverending paragraph that I missed it. All my fault.