Re: 1973 18 hp Evinrude starts out running great, but slips out of gear
"Link and Synch" just refers to coordinating the amount of gas being delivered by the carb to the proper amount of spark by the motor. No good dumping more gas in the cylinder, if it can't be ignited properly. As the butterfly valve on the carb opens to deliver more gas, you want/need to fire the plugs more frequently. When you twist the throttle it turns the armature plate which causes the motor to fire more frequently. At the same time, there is an adjustable crescent shaped cam on the front of the armature plate that pushes on a roller. This roller is "linked" to the butterfly valve on the carb so that the motor fires more often it gets more gas simultaneously. I found this post from the might Joe Reeves, so I'm just going to copy and paste the link and synch procedure here:
Joe Reeves:
" Timing is set by the flywheel/crankshaft key. If the key isn't sheared, the engine is in time.
The full spark advance is also set.... the armature plate (plate the points are on) turns as you apply throttle, and continues to turn until it hits a stop built in on the block. There is no adjustable full throttle spark advance setting.
The rod linkage leading from the armature plate to the throttle cam roller? Read on.......
(Synchronization Of Older 2 Cyl Engines)
(Such As The 28, 33, 40hp Etc models )
On the linkage that runs from the armature plate (the plate the coils & points set on) to the carburetor throttle roller, loosen the set screw on the brass collar that you see there and temporarily move it away from the armature plate/vertical throttle arm clevis (clevis is that thing the linkage rod slides through). We'll refer to that vertical throttle arm/armature plate clevis simply as the "clevis" from this point on.
Look at the cam that's attached to the front of the armature plate.... the cam that slides up against the carburetor throttle roller. You'll notice that there's a scribe mark on it. Also notice that at the top portion of the intake manifold there is a raised portion, that top portion forming a point. The carburetor roller should contact the cam and just start to open the throttle butterfly when the scribe mark is dead center with that point.
With the engine in gear (not running of course) have the armature plate advanced all the way (by hand) so that it is up against its stop. Now adjust the brass collar (set screw) on that associated linkage rod so that it is up against the clevis. It should be adjusted so that there is either no play, or just a hairs play between the collar and the clevis.
At this point, the armature plate movement is not advancing the throttle butterfly via the rod movement, but further movement of the throttle control, although the armature plate cannot move any farther, causes the tension spring at the armature plate to allow the vertical throttle arm to move farther which now advances the carburetor throttle butterfly via the rod. When fully advanced (full throttle), the carburetor throttle butterfly should be fully opened (horizontal).
If all else with your engine is as it should be, that should do it.
And..... don't take your engine to that fella again (grin).
Oh, also.......
(Point Setting Of Magneto Models)
(J. Reeves)
Set the points as follows. Have the flywheel key aligned with the fiber rubbing portion of the ignition points. Adjust the gap so that a .020 gauge will pass thru but a .022 will not. Should there be any question of the points being dirty (touching the contact with your finger would cause them to be dirty), clean them with a small brush and acetone or lacquer thinner.
NOTE: Should the operating cam have a small portion on it with the word "SET" imprinted, align this portion with the fiber rubbing portion instead of the flywheel key. "
Holler if you get stuck again. You'll get it!
