Shake rattle and no roll 1994 Johnson

[BRUNO]

Thought I would see if the any of you had experienced the problems I am having with a 1994 120hp Johnson. Last year when I ran it it would run fine up to almost ¾ throttle. AT that point it would bog and start to shudder and shake. I rebuilt the carbs and took it out last Friday. Started fine, idled great once it burn off the fogging oil. Get up to ¾ throttle and it started sputtering again. Plugs are new, gas is too. Ran just great at ½ throttle and lower. Now I did notice that the throttle itself pushes smoothly until it reached that ¾ open position. It then becomes hard to push and I have not forced it. Plan on looking at it again this weekend. I seem to remember in my 1969 Pontiac Lemans convert , 350 CI , 335 hp, that when the timing chain slipped a notch due to the desire to go fast NOW that it then burbled and burped like the outboard. Is there a mechanical vacuum advance on this outboard. Any advice?

[Surface Tension]

When you said the throttle hangs at 3/4 then shudders, I wonder if you have something interfering with the mechanical advance. Pop the hood off stick it in forward and look to see whats going on when you advance the throttle. Look for the throtle limiter hitting and binding or a plug wire in the way. All done in the driveway with the engine off of coarse

[danfall]

I'll second surf. First thing is to rule out mechanical issues. Moving parts always fail first.

There is nothing in the non-mechanical motor function that I can think of that would restrict the physical movement of the throttle.

Put it in gear with the motor off and compare. If you are binding up at 3/4 throttle, find the cause. If not, look at all the mechanical items that impinge against the throttle when on and you should be able to rule to one or two items.

Another option is to call that old TCO shop in Shakopee, they haven't let me down, yet.