1973 Merc 850 Timing advace

[ShowMeGuy]

What is the max timing advance on my 1973 Merc 850? SN 3740426 Is it max 21 or 34 deg?

I'm going to do this this evening.
http://forums.iboats.com/showthread.php?t=168855
But had a questions on the Max timing advance portion comment below.

Timing Event Two - max advance.
As you continue to advance the throttle the timing will advance while the carbs slowly open a bit more. The next adjustment is max advance, this is the point where the distibutor (or trigger) can advance no more. Set the max-advance stop to 21 degrees for "direct charge" crossflow inlines and 34 degrees for the older plain vanilla crossflows. Use the light, - err to the side of caution.

TIA!

 

[merc850]

Re: 1973 Merc 850 Timing advace

According to the Manual it's 27* BTDC.

 

[Chris1956]

Re: 1973 Merc 850 Timing advace

I vote for 21* BTDC for your 1973 Battery powered Distributor/CDI unit. The vanilla crossflows were a few years older.

 

[ShowMeGuy]

Re: 1973 Merc 850 Timing advace

OK guys.. I"m prolly just tired but I got started on the timing/sync stuff tonight and was stumped on the first part.... ugh!
I have four what I'll call set screws with rubber on the ends.... I confident on 2 of the 4...
Pretty sure these ones below.
I have the minimum stop where the distributor stops when the throttle is at idle...
I have the max advance screw where the distributor stops turning all together and stop timing advance.
These I'm not so sure.
I have a screw that I think is for the first initial pick up of the throttle but then i have another on the left side of the motor that I don't really know what it does....
PICS in the AM I promise! Hpefully my SM is here tomorrow!! ugh!

 

[ShowMeGuy]

Re: 1973 Merc 850 Timing advace

OK guys here is a pic of the "stop" that I'm not sure about. The adjustment under the grease zert towards the TOP. Is this the one that I need to adjust to get the first throttle pick up?

I think after this AM when I looked at this plate I have the rest of them figured out.
Top Left is Maxium Throttle. (which should already set as I did that first.)
Bottom Left is the Maximum Advance (which i'll set to 21deg)
Bottom Right is the Idle Stop (I'll follow the setting on the link above)

Got the battery on trickle charger today so I'll be set after work to get this set I think....

 

[Chris1956]

Re: 1973 Merc 850 Timing advace

That link under the zerc may be needed if you cannot get the idle pickup setting correct. I never needed to use it, and I think it went away in the later distributors. The other settings are idle stop (Idle speed setting), Throttle stop (Max throttle opening) and Max Spark Advance (S/b at 21* BTDC, as previously recommended). The brass collar sets the idle pickup timing (s/B 4-6* BTDC), via loosening the two set screws under the collar on the midsection of the distributor.

Throttle stop should be set so the throttle stops opening just before the carbs are wide open. This protects the carbs from damage, when you hammer the throttle.

Set the idle stop to 800RPM or so. Adjust the throttle cable to push the throttle closed and add a bit of preload. It will help you find neutral.

 

[ShowMeGuy]

Re: 1973 Merc 850 Timing advace

The brass collar sets the idle pickup timing (s/B 4-6* BTDC), via loosening the two set screws under the collar on the midsection of the distributor.

That brass collar you are mentioning for the idle pick up timing as I haven't heard or read of that yet in my research.... So I'm clear on what you are calling idle pick up, is this when the first arm comes in contact with the throttle arm? OR what that link is calling Timing Event One - throttle pickup.

Thanks for the help this AM!!!

 

[Chris1956]

Re: 1973 Merc 850 Timing advace

Carbs should just start to open when the distributor is at 4-6* BTDC. So set the timing to 4-6* BTDC and then adjust the brass collar until it just touches the carb lever. Lock it down and leave it alone.

 

[ShowMeGuy]

Re: 1973 Merc 850 Timing advace

Perfect. That is what I was getting ready to do after I looked at it all.... but got to second guessing myself... thanks Chris!
***BEERS to you*** Cheers.

 

[ShowMeGuy]

Re: 1973 Merc 850 Timing advace

She is running/purring great at idle.... More to tell tomorrow... Had to sort out a fuel leak issue today... that is done.. Just prettying up the motor now... BLAM.