You are here:

Boat Repair/motor runs like it is running on two cyl.


QUESTION: I am working with a Mercury 4 stroke 2000 90 hp.  I run two bat. on the boat, Bat.1 for starting the motor and Bat.2 for accessories, they are hooked to a perko switch that reads 2 all 1 off.  The instructions said to never switch it to off with the motor running or you would damage the charging system, this was the only warning. The last time out I ran the #2 down very low and wanted to charge it up, so after we were under way I switched from Bat.1 to Bat.2 so it would charge it up, shortly afterward the motor started to run like shit, I switched it back to Bat.1 and it still runs like shit,like it is running on two cyl.  I have done this before without a problem, but never with the bat. so low, can this damage ?  The next day I used my timing light to check for spark, the motor starts easily and idles fine, but it seems like #2 and #3 don't have spark at idle, but off idle they fire fine.  This is the first Mercury I have owned and I have only put 20hrs on it since I got it, so I am not that familiar with it.  The way it ran coming in was like i had a fouled plug and dropped a cylinder... the plugs look good.  any thoughts?

ANSWER: sounds like you have a bad stator. it is under the flywheel and it can be checked with a peak voltage meter.or ohm meter to test for a short to ground...high side 130 ac volts or higher..low side 40 ac volts or higher..

---------- FOLLOW-UP ----------

QUESTION: so switching to battery two caused a problem with the stator and that is why two cylinders have no spark at idle but have spark off idle? I thought the purpose of the switch was to be able to charge both batteries by being able to choose which one the motor was running off of. did I miss something?

Ok the battery switch should not be moved while the engine is running because it could cause a problem with the charging system as it did with yours..  the stator is a part of the ignition and charging system of the engine..
the stator and regulator/rectifyer should also be checked..

Boat Repair

All Answers

Answers by Expert:

Ask Experts


Everett Peacock


Marine repair questions


35 years experience

Taught Marine electronics at NOVA CC IN ALEXANDRIA VA

certified, Yamaha outboards,yamaha stern drives, Mercury outboard, Mercruiser, Evinrude. Johnson, Mariner, suzuki, Volvo Penta, Honda,

Awards and Honors
service exelence award ( yamaha)

©2016 All rights reserved.