1972 Evinrude 100hp Starflite dies at quarter throttle

[Matt Mann]

I just bought this motor so I have no history on it. It starts up just fine, idles fine. In the driveway on the muffs it revs up fine. On the water, at about quarter throttle (10mph on my 21 ft. boat)...it will just die when I give it more throttle. If I back it off to quarter throttle it will run all day. I cleaned the carbs and I have spark on all 4 (although I haven't checked spark as it is dying). Good compression at 120 each cylinder. Any ideas?

Also: I would like to know what the tiny switch like device is that rides the cam on the throttle arm (see middle of photo). It doesn't seem to do anything. The two leads always have continuity because they are connected by a piece of metal. It always seems to have continuity to ground. What is it? How does it work?

Thanks,

Matt Mann

 

[Joe Reeves]

Re: 1972 Evinrude 100hp Starflite dies at quarter throttle

That small switch is a safety ground switch for the starter solenoid. When throttle is applied, the continuity is broken which in effect disables the starter solenoid. If grounded permanently, it would be possible to start the engine in gear at full throttle..... not a good idea!

There are two brass fixed high speed jets in each carburetor, located in the center bottom portion of the float chambers.... in back of those 7/16" hax head side screws. If you haven't cleaned them manually with a piece of single strand steel wire, do so.

Let us know what you find.

 

[Matt Mann]

Re: 1972 Evinrude 100hp Starflite dies at quarter throttle

It ended up being the flywheel key. I replaced it and tightened to torque and it ran fine after that.

 

[F_R]

Re: 1972 Evinrude 100hp Starflite dies at quarter throttle

Somebody has defeated that safety switch in the picture. That wire going to the lower terminal is not supposed to exist. At slow throttle settings, the upper terminal is grounded through the switch base. At fast throttle no grounding exists, so the starter won't crank.

Betcha the switch is burned up----that's why somebody defeated it. OK, so they got it working, but the purpose is non-existant.