1978 mercury 900 timing issue

[Glastron Fisher]

So ive been fighting this issue since I replaced the distributor, I cant seem to figure out how to set my timing at idle, I know how to set Mac timing but can't figure out idle timing, it needs to be between 4-6 BTDC and I've searched the manual but it's black and white and I can't see exactly what they are talking about. Thanks in advance

 

[CharlieB]

Re: 1978 mercury 900 timing issue

Check the 'Stickies' at the top of the forum, Clams posted a step by step guide of adjusting the stacked 6's that applies to most every one of the distributor ignitions, all were almost identical setting.

 

[Glastron Fisher]

Re: 1978 mercury 900 timing issue

Ok I'll check those, I think I figured it out tho after 3 hours of staring at my old distributor

 

[Chris1956]

Re: 1978 mercury 900 timing issue

There are two 5/16" bolts on the dist body(heads facing down), about 1/2 way up. Loosening those allow the idle timing collar to rotate to set the idle timing. Is that the part you missed?

 

[Glastron Fisher]

Re: 1978 mercury 900 timing issue

Yes, the manual was too confusing about that part and pictures were horrible, I messed with my old distributor out of the boat for a few hours befor rinsing that out, and does anyone happen to know timing at idle? It's 4-6 but is it BTDC or after? I swear it was BTDC but read somewhere about timing advancing to TDC then BTDC in like explaining how timing works but I think that's just in general, the boat starts perfectly now and I just have to adjust max timing out on the water at some point

 

[CharlieB]

Re: 1978 mercury 900 timing issue

After, as throttle is applied timing approaches TDC increasing engine speed, timing is BTDC as the carbs actually begin to open.

 

[Glastron Fisher]

Re: 1978 mercury 900 timing issue

Ok, I think mines set at 5 degrees after TDC then, I'll check again tomorrow

 

[CharlieB]

Re: 1978 mercury 900 timing issue

The actual # is not important as the actual idle speed in gear and in the water. Out of the water and no load idle speed will increase, not to worry.

 

[Glastron Fisher]

Re: 1978 mercury 900 timing issue

My idle speed is about 1000 rpms, drops to about 650 or 700 in gear, I want to get it down a bit more as i hear it going into gear and it doesent grind but it crunches, is that ok?

 

[CharlieB]

Re: 1978 mercury 900 timing issue

Do NOT 'ease' the shifter into gear as that will allow the straight cut engagement dogs to 'bounce' and chatter before solidly engaging.

Firmly and positively shift fully into gear.

Check to ensure the carb linkage allows all throttle butterflies to bully close. Each butterfly is drilled to allow only a measured amount of air at idle. Idle speed is controlled by ignition timing.

 

[Chris1956]

Re: 1978 mercury 900 timing issue

GF just to be clear. Idle pickup timing is 4-6* BTDC. So just as the carbs start to open, your timing should be 4-6* BTDC. Max spark advance is 21* BTDC.