1977 Evinrude 75hp- need help with service manual link & sync

[BonairII]

Motor ran well the first time I took it on the water. 2nd time out, I dropped a coil (hopefully new coil solves that problem.

Before I go back on the water, I want to verify that the link &sync and throttle cam etc are correct.

The service manual seems pretty straightforward, but I've got a couple things I'm not clear about.

First- When explaining the throttle cam adjust, the manual states something to effect of "when the cam roller contacts the cam, yadda yadda". Does this mean that there is a throttle position where the cam and roller AREN'T in contact? Because the way it's set up now, the roller is always in contact with the cam.

Second- The manual states to use a timing light on #1 cyl and start motor. Then adjust idle stop screw til TDC mark is aligned with the pointer. What does idle speed have to do with timing? :confused This will be the first time I've ever used a timing light, so I want to understand what I'm doing....and WHY I'm doing it.

Here is the info straight from my manual:

 

[BonairII]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

Anyone?

 

[BonairII]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

120 views and no replies?

Am I asking a dumb question...or is there no one that's done a link&sync on a 1970's 70-75hp motor?

 

[BonairII]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

Has no one done a link and sync on this motor before?

 

[F_R]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

Take it easy, I just now saw your post.

OK, the roller should not be in constant contact with the cam. At throttle settings less than the mark alignment, the roller should not be in contact. Perhaps your idle speed is set so high that you can't move it enough to break contact???

Timing has everything to do with idle rpm. Once the carb plates are closed, idle speed is controlled entirely by spark retard.

I'm really not sure what the book is telling you about the TDC mark. You didn't post that page, did you?

 

[BonairII]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

idle speed is controlled entirely by spark retard.

I def need to redo the link & sync cause the cam is always in contact with the cam as I have it now. Motor fired up very quickly, but the idle is much higher than it was before I did the link & sync.

On a side note: For some reason water wasn't pumping the 3rd time I started the motor. Impeller/key was fine...telltale not plugged...and I back flushed the intake pipe and water came out the telltale, so I have no idea why I wasn't getting water. LU will be back on in the morning, so hopefully all is well with cooling now.

Here's the page I forgot to post

 

[Rayandrewss]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

Bonairll......I had a heck of a time setting my link & sync on my 79 35hp. The original OMC manual didnt explain it very well ( well, to me anyways) I have no timing light so I did the best I could. I actually looked up a You-Tube video of a Link & Sync and got some good ideas from there. I didnt unhook anything but just kept adjusting the screw where the linkage was hooked ( catch my "cough/sneeze" thread under my name) it's real close to running right ( I'll know better in a couple hours as I am taking it on the water this morning). Be patient waiting for answers, once they start, the great guys on this post won't leave you alone till you get it right.

 

[Haffiman]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

What is described above is 'Pick Up Timing', and will not be the real timing at idle.

1: Verify with Cyl 1 at top (TDC) that the arrow aligns with TDC at the flywheel.
2: Start the engine with timing light hooked up to cyl 1.
3. Adjust the 'Idle stop screw' until flywheel marking TDC aligns with arrow.
4. Stop the engine and adjust the yoke so the mark on the cam aligns with the roller on the carb, tighten the roller screw.
5. Start the engine, put in forward gear, boat moving freely and adjust the Idle Screw so an RPM of 750 is obtained.
This may result in a gap between the roller and cam, but is correct!!

 

[F_R]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

OK bonair, you asked for the WHY. Here's why: Beginning with the throttle position where the cam mark is aligned, as you mofe the speed control toward fast, the timing plate starts to move, advancing the spark. At the same time, the carburetors slowly begin to open to admit more fuel/air. At some point, the timing plate reaches full advance position (up against the full advance bumper). But the carburetors are only partially open. THAT is the "Cruise Throttle" position, which gives the best horsepower for the fuel being consumed. Continuing to move the speed control toward fast, the carburetors are kicked wide open. That gives the maximum horsepower the motor can deliver, which also gulps fuel.

Going the other way with the speed control, first the carburetors return to the cruise throttle position, then both the spark advance and carburetors slowly return to idle position, in a controlled sync built in by the engineers. Once it reaches the point where the cam mark is aligned, the carburetors are closed tight, and no longer respond ot furher speed control movement toward slow. SO, any further speed control movement only retards the spark----the amount of spark retard is actually what is determing idle RPM.

NOW, back to that cam and mark. The carburetors must not begin opening too soon along the spark advance curve. If they do, the airflow through them is insufficient and the fuel/air ratio will be too lean, and the motor will hesitate or stumble (even die if too far off). To get it right, the engineers have provided a way of setting the exact point at which the carburetors start to open. That is what you are setting with the sync procedure. Furthermore in previous years, the setting was just accomplished by the length of the rod and yoke. In your motor, they go a step further and tell you to fine tune it by adjusting that yoke so the cam mark and roller meet just as the timer plate provides a spark at exactly TDC, which is where they determined the carburetors should start to open. Yes that is usualy called pick-up timing. Kind of misleading since you aren't changing spark timing, you are changing the time the carburetors start to open as related to the spark moment

Hope this is clearer now. Frank

 

[BonairII]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

Going to give this all a whirl later today, I'll keep you posted.

Can I use the timing light in bright daylight...or do I have to wait til it's a bit darker out to see the light strobing on the flywheel?

 

[Haffiman]

Re: 1977 Evinrude 75hp- need help with service manual link & sync

Should not be a problem in daylight.