Link & Sync and Timing Question

[scout-j-m]

I have a running thread on here for my 1994 70hp rebuild (linked). In it I am all the way to to setting the timing, almost ready to crank up for the first time. I set the WOT cranking timing to 32 deg easy enough. However, when I backed the throttle back down to idle and rechecked it I was getting 6-8 deg. Since I have not even started it up yet the idle hasn't been adjusted and the roller cam is not touching the eccentric screw roller either. When I reinstalled the towershaft earlier I did not back out the idle adjustment screw on the towershaft at all so when I began to do the carb adjsutments I wasn't exactly starting at "zero". So my question is should I disconnect the throttle linkage cable, screw out the idle adjustment screw all the way, reinstall the throttle cable on linkage, and readjust the cam roller like I did earlier? If so and I reset the WOT cranking timing to 32 degrees would I likely see it as 0 degrees at idle position? I understand the timing can be advanced a few degrees at idle but the way I had it before seemed like I would be closer to 10 degrees or so by the time I adjusted the idle screw out even more to achieve the correct idle when I got around to running it, especially since at the current idle screw setting the cam wasn't even touching the carb roller.

 

[scout-j-m]

It really has me wondering since I have not seen anywhere in my 2 repair manuals or on this site that the idle screw must be initially set all the way out before doing all the adjustments. It seems like it should so maybe it is just assumed everyone would do that.

 

[Jiggz]

Read this topic to mechanically zero the tower, carbs and idle settings.

http://forums.iboats.com/forum/engi...timing-a-1998-force-120-runs-terrible-at-spec

 

[scout-j-m]

Thanks Jiggz. Looks like I goofed up doing what I did! I will fix it tonight and report back how it goes.

 

[Jiggz]

Although it is absolutely true that the control tower mechanically moves (advances and retards) timing of the electrical spark linearly with the carbs throttle position, however, when you make adjustments of the timing with the timing rod (on top of the control tower) nothing is moved mechanically (except for the position of the trigger advancing plate), i.e carb throttles, idle screw, etc do not change position instead the only thing that is moved is the timing of the electrical spark (relative to the position of the trigger advance/timing plate).

On the otherhand, when you make adjustments to the idle screw, link rod, cams, eccentric screw, etc. it also affects the position of the electrical timing (because the control tower is mechanically linked to all these parts thus also moves when mechanical adjustments are made, hence also adjusting the electrical timing.

 

[scout-j-m]

Yeah, it all makes sense now. I knew something was off when, in order to achieve 32 deg wot cranking timing, I had to really screw the timing adjustment screw in a long ways and the arm from the trigger was getting pulled it very close to where it attaches to the towershaft connection.

 

[Frank Acampora]

Did you not watch my video on synchronizing timing and carbs? It explains it quite well. 32 degrees is OK if you always use pump gas. 30 degrees is better especially if you will use Marine gas, but if you static time the engine you need to set it to 28 to achieve 30 degrees while running at WOT.

Timing at idle will vary upon health of the engine, prop pitch, and a number of other factors. Timing at idle is NOT important except ( if really out) to tell you that something is out of whack. The only important setting is timing at wide open throttle.

Now some Mercury ignition engines will give a spec for timing at WOT and timing at idle. However, the timing at idle is not a hard and fast number. Rather, if not close, it tells you that you did something else wrong.

 

[scout-j-m]

Did you not watch my video on synchronizing timing and carbs? It explains it quite well. 32 degrees is OK if you always use pump gas. 30 degrees is better especially if you will use Marine gas, but if you static time the engine you need to set it to 28 to achieve 30 degrees while running at WOT.

Timing at idle will vary upon health of the engine, prop pitch, and a number of other factors. Timing at idle is NOT important except ( if really out) to tell you that something is out of whack. The only important setting is timing at wide open throttle.

Now some Mercury ignition engines will give a spec for timing at WOT and timing at idle. However, the timing at idle is not a hard and fast number. Rather, if not close, it tells you that you did something else wrong.

Thanks Frank. I watched your video but it was probably a couple weeks ago. I don't recall the actual timing numbers though. I was just going off of the service manual...which maybe I had it backwards and was setting to 32 degrees static when I should have been setting to 28. Anyways, what I use ethanol free 87 octane pump gas? I have a local station which I use for every carb operated engine I own.

 

[emtlarmy]

Sorry for asking but I'm very new at outboard motors... I have a 1995 70 hp Mercury force. I am trying set time but haven't found anywhere I can get firm numbers. Is the 32, 30 or 28 BTDC you say here good for mine as well?

 

[Jiggz]

Based from my service manual the 70 and 75 HP Force are set to 32 BTDC static meaning at cranking speed. And the 85 and 125 the static should be set to 28 degrees.

 

[emtlarmy]

Thanks