1998 Evinrude 90 HP SPL Surging Mystery

[blairhj]

Fuel System Checked:
Fuel lines good, fuel tank vent unobstructed, primer bulb hold pressure, no line leaks, fuel pump tested w/ fuel line pressure gauge w/ 10 psi, new fuel, no water in tank, all gear oils new, engine at correct trim, no one in front of boat/no cavitation, battery cables intact on new battery, spark plug wires appear intact (arching test tonight), new plugs, no over heating, ect, ect.

Motor surges from full power to redacted power at any point past 1/2 throttle. Will stay at desired power for 3 to 4 seconds, then back to lower RPM for 10 to 20 seconds, then back to full power.

What ghost to chase next.....power packs or ?

 

[racerone]

Run with a timing light 1 cylinder at a time.----See if spark is lost and then returns.-----Post the compression test results here.

 

[blairhj]

Run with a timing light 1 cylinder at a time.----See if spark is lost and then returns.-----Post the compression test results here.

I took a meter to each individual ignition coil checking both primary coils and secondaries for resistance. Found two bad coils and just ordered all four and new wires so I'm starting fresh. I don't suspect the power pack and am hoping this is/was the culprit. Compression was done months ago, don't remember but do remember all four cylinders were high for it's age and with in the percentage guidlines.

Thank you for replying sir

 

[blairhj]

I took a meter to each individual ignition coil checking both primary coils and secondaries for resistance. Found two bad coils and just ordered all four and new wires so I'm starting fresh. I don't suspect the power pack and am hoping this is/was the culprit. Compression was done months ago, don't remember but do remember all four cylinders were high for it's age and with in the percentage guidlines.

Thank you for replying sir

And Racerone, what you said to look for IS exactly what I summize was happening to cause that surge....ran on all 4, then 2, then 4, and back and forth.