1995 Mariner; Will only run up to 4100 rpm @ WOT

[sroy]

I own a 1995 17 ft Tracker Nitro with a Mariner 115hp, 4 cylinder; S/N - 0G175997. Before this condition I am about to describe the motor would run about 53 mph (gps) @ 5800 rpm. The prop is a three blade (22).

Recently, something change where I now can only run about 39 mph @4100 rpm.

I have replaced the spark plugs, spark plug wires, fuel filter; no change.

I have performed a compression test and all 4 cylinders measure 134 to 135 psi.

I have measured the resistance of the 4 coils, primary and secondary and they measure in range according to the Mariner Shop Manual. I have also measured the resistance of the Red Stator (Green/White to White/Green) @ 691.4 ohms.

I have measured the DVA voltages from the Red Stator and the Red Stator Adapter
295 @ idle and 320 @ WOT .

I have measured the DVA voltage output of the switch box to the 4 coils.
#1 195 @ idle 204 @ WOT
#2 195 @ idle 240 @ WOT
#3 195 @ idle 200 @ WOT
#4 195 @ idle 240 @ WOT

The kill lead reads 320 @ WOT.

So far, the only unusual reading is the output of the switch box to coils #1 and #3 are reading about 16 % lower than coils #2 and #4.

Would this difference be enough to prevent the motor from reaching 5800 rpm?

 

[flyingscott]

Your top RPM for that is 5250. I would check the carb linkages make sure the carbs are opening and nothing is broke a lot of plastic pieces on those.

 

[sroy]

Thank you flyingscott for your response. I forgot to disclose that I had verified that all 4 butterfly valves were fully opened at WOT. Does the indication of lower DVA voltages on the primary of coils #1 and #3 verses coils #2 and #4 cause the motor not to reach full rpm? Also, did you find that rpm (5250) from a table or calculation? How is that determined?

 

[flyingscott]

The RPM recomendation for your motor is 4750-5250 that is straight from mercury. I owned the 125 version of that I would go to www.cdielectronics.com to find the trouble shooting guide for your ignition. You could have a stator problem in the high speed windings that is a common problem to them. Or it could be the coil windings.

 

[Faztbullet]

Well it not the stator as the other cylinders have correct voltage and all the high speed winding is doing is charging the capacitor. I suspect its switchbox SCR's or the internal rectifier has a problem on those two(they are paired in trigger).