115 Mariner Loss of RPM under load

ReelSmokin · #1 August 8th, 2007, 10:45 PM

I have a 115 Mariner inline 6. Recently I had the stator replaced and the engine ran great. After 4 trips I lost RPM and now only top out around 4200 but only under load. In dry dock I can redline it up to 6000. Even in the water at 4200 it sounds good, no misses, vibration, or jerking. I checked fuel by spraying gas into carbs while at top RPM and engine bogs so I iliminated that. (By the way dangerous) I checked all the pulgs, none seem to be burnt and all had a little wetness to them which is normal. Good compression in all cylinders as well. I have run out of things I know to test. Any suggestions.

renny1 · #2 August 9th, 2007, 03:56 AM

you dont say what year but i had the same trouble and it was the mixture screws on the carbs but i`m sure the experts might have a different opinion
i followed the settiung up of the carbs in the clymer manual an now she is running at 5100

Laddies · #3 August 9th, 2007, 09:08 AM

Idle mixture screw effect idle only not top end, you could be rich on top end caused by a leaking inlet needle or a leak in the secondary pump diaphram, have you pumped the bulb to see if it has a effect on the problem? you might have a shorted rectifier causing the problem disconnect the 2 ylellow wires at the rectifiier to ck this, or a bad bias in one switchbox causing the problem

ReelSmokin · #4 August 9th, 2007, 05:15 PM

The rectifier is my next step. I wasn't sure how to test it and didn't want to chance hurting anything by running the boat without it connected. Is this really a good idea?

Tadd_P · #5 August 9th, 2007, 05:50 PM

well.. manual tells ya how to test the rectifier. So they wouldnt put it in there if it were to harm the motor. I have a 115 inline 6 mercury and had similair problems and changed my rectifier anyways. Solved 2 of my problems in one. I also had a problem with my battery going dead oh every 4-5 trips out on the water. Changed the rectifier and gained my 10 mph back and havent had to charge my battery yet so id buy a new one. Dont cost that much to replace is the way i looked at it. Being a 1979 doesnt hurt to replace parts once in a while. Good luck

ReelSmokin · #6 August 12th, 2007, 11:35 PM

Well I tested the rectifier and it did in fact have a bad diode. Friday I was able to pick up a new one and install it. I couldn't test it until today and I am still having the same problem. Max RPM is 4200. Does anyone know how to test the two switchboxes? The manuel I have doesn't give any instructions for it.