1962 Evinrude 40HP Idles Rough/Misses at High Speed

1962 40HP Evinrude Lark IV

Idles roughly and stammers at high speed (power head shakes).

Compression is equal. Timing advance to throttle is set at pointer, new coils and points, verified timing with timing light, runs independently on each cylinder but neither runs smoothly independently.

Running out of ideas. Any diagnosis advice/help would be much appreciated.

Thanks,
Tom

Hi Tom, welcome. Have the spark plug wires been checked for abrasions, spark leaks? Are they original?

Spark leakage is easiest to spot when the motor is run at night with the cover off.

The armature plate that the points etc set upon.... Does it have a wobble to it, up on one side, down on the other, back & forth?? If so, the point setting will definitely change as the throttle/timing is increased. Other than buying new parts, the following may be of interest to you.
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(Magneto Armature Plate)
(J. Reeves)

If the armature plate has a a loose fitting, wobbling motion (the plate that the points, coils etc are attached to), it is usually caused by a slightly worn support ring. This allows the point setting to change erratically as the armature plate turns.

The cure is to remove the armature plate so that the support which is attached to the powerhead with 4 screws is visible. Then, with a screwdriver and hammer, or some tool of your choosing, and looking straight down at the support ring, make a slight indentation at what would be called the 12, 3, 6, and 9 O'clock positions. Install the armature plate and check for a smooth turning wobble free movement.

You may need to do that procedure a few times to obtain the proper fit (not too tight, not too loose), but it's worth the effort.

Use a small amount of anti corrosive grease between the aluminum ring and the brass support plate and also on the brass bushing of the armature plate when all is well.

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Great trick, Joe. I go 12, 2, 4, 6.....and so on. No, that's not how often I pee at night. At least not yet.

Seems like we're birds of a feather on various tricks Tim. The other function.... after a bout of blabber & prostate cancer, at about 3am I just reach down and feel that urostomy thing. If it's full, I get up.. if not...........
ZZZZzzzzzzzz!