Throttle issues

I have a 1978 35hp evinrude that won't open up all the way, it runs good and starts good it's just the tiller won't open the butterfly in the carb fully, any help is appreciated.

You may have the throttle activating rod set wrong.... see below:

(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.

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Thank you joereeves! I will look this afternoon, and hopefully get this resolved. I am looking for a starter for it if you know any good parts places?

Apparently I have another issue... Could it be the tension spring? I did notice the tiller doesn't twist no more than a quarter of a turn, unlike my 20hp that goes much further. After advancing the armature plate by hand the carb roller now contacts the cam, but unfortunately that's about as far as it goes the tiller handle doesn't open it up anymore. For giggles i tried to turn the plate he opposite direction of what the throttle would turn it (in the race car world the term is "retard the timing") and then set the brass set screw and then it would open up fully. Or should I simply take it in and spend too much on an old motor?

It must be in forward gear to advance the timing fully, the shift lock lever may be out of adjustment or it is not fully going into forward gear. Engine sync is the carb butterfly should just begin to open when the roller is center of the two marks on the throttle cam.
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There are three notches on the bottom of the lever and the detent for the shift lever needs to be center of each notch in its perspective gear. It does two things it keeps you from over reving the motor in neutral and it also keeps you from shifting out of gear at high rpms.

The adjustment of the brass stop on that rod must be understood.---------You can not just set that where it " looks right " to you.-----------And the motor must be in gear to get full throttle travel too.

The way I like to describe the link adjustment is with the engine off shift into forward gear and then give it WOT. loosen the screw in the brass collar and with one finger push the throttle butterfly wide open and push the collar up tight against the pivot pin and tighten the screw it should hold the throttle butterfly wide open.

That throttle advance rod can only be adjusted one way, as I stated above, taken from the manual many years ago.

If that doesn't correct your problem.... look closely as you have an additional problem.

I agree joereeves there is another problem, I will keep looking at it I'm sure it's an easy fix once I find it.

The motor is in gear fully...

Holy crap I found the issue! The bracket for the electric starter was missing 2 bolts and crooked causing the throttle linkage to hit.. Ordered new bolts for it and put them in last night, woks like champ. Thank you guys for you help.

We knew you could do it!