1977 Evinrude 115 rough idle and miss at high rpms

[wiliermdb]

Purchased a 1977 Glastron CVX 16 with the original 1977 Evinrude 115 on the back.

Brought it in to have it tuned and it's still doing the same thing. Rough idle especially in NO WAKE ZONE and rough under load to plane. At upper RPM range, (5000 - 5500) it will surge a little. If I nail it to the floor, it'll jump out of the water and be up to 40 MPH in no time. Throttle response is good. Running at 3500 and nail it, it jumps up and the boat is moving.

Mechanic changed plugs to the correct Champions, rebuilt carbs, set timing and that's about it. I did notice this morning that two coils on cyl. 2 & 4 have some small cracks on the tops and into the sides. Hair lines. Not huge. These appear to be Mallory by the "M" symbol on the coil.

Cylinder #1 has a green colored coil, which I'm assuming is a Sierra from what I've seen online, and cylinder #3 looks to be an original.

Compression is 135 on #1, 125 on #2, 135 on #3 and 120 on #4.

Where do I go from here? Is it possible that the coils are heading south? I've had that happen with a car before that had separate coils and a bad plug wire. What areas should I be looking at?

Thanks for any info.

Marc

 

[tashasdaddy]

Re: 1977 Evinrude 115 rough idle and miss at high rpms

99% coils going bad. but, have you checked compression?

take an induction timing light, clip it on to each spark plug wire, and run the boat in all ranges. just point the light at the opposite hand you are holding the timing light. watch for a missed spark, or unconstant spark. do this on all plug wires.

it also could be as simple as a bad plug wire, arching to the block. (slight crack in insulation) run the motor in the dark on muffs, what for a spark from plug wire to block.

 

[ezeke]

Re: 1977 Evinrude 115 rough idle and miss at high rpms

If it were mine, I would:

Replace the coils if they are in any way distorted in color, cracked or melted. If they are bad they can destroy the powerpack;

Check the timing. It should be set for full throttle spark advance of 28 degrees;

Test the rectifier;

Re-check the flywheel nut for 105 Ft. Lbs torque;

Test the fuel system for air leaks, including the fuel pump.

BTW, the M on the coil is probably the OMC stamp, not Mallory.

 

[wiliermdb]

Re: 1977 Evinrude 115 rough idle and miss at high rpms

I'm no mechanic but I'm leaning towards the coils as one reply mentioned. It appears that at least two have been replaced in the 33 years this motor has been around.

I'm just going by what I've seen in cars over the years.

Any issue with using either all Sierra coils or all Mallory or should I go with all OEM coils?

Compression is listed in the original post.

Thanks for the responses. If it turns out to be the coils, I'm going to request at least a partial refund from the mechanic. That's what I'm paying him for, to FIX the problem.