still_bill
Contributing Member
I have purposefully left the title vague because this unusual defect could happen to any brand, make, or model. For almost 2 years, I have struggled with loss of spark on one bank (3 cylinders) on my V6 Yamaha 1989 200HP 2-stroke.
See my original posts here: https://www.thehulltruth.com/boatin...a-200hp-2-stroke-no-spark-port-cylinders.html , and here: https://www.marineengine.com/boat-forum/threads/1989-yamaha-200hp-no-spark-on-port-bank.479827/
It turns out that the problem was due to factory defect on "Jetunit" brand stators. The stators are simple - they have 3 coils (circuits). One gives the voltage for charging the battery. The other two feed the CDI ignition spark (charge coils). There is a high rpm, and a low rpm, charge coil. Each is simply a coil of wire, and the flywheel magnets pass by them and generate voltage for the CDI. So, there are four color-coded wires (two for each charge coil). These wires attach to the CDI box at terminals 1-3 and 2-4. You can test the stator by measuring the resistance of each coil. In my case, the new stator tested as "good". I found eventually that disconnecting either charge coil resulted in the engine running on all 6 cylinders, but with poor high rpm performance, or hard starting and poor idle (depending on which charge coil was disconnected). So, for over a year, I ran with just one coil and suffered with the hard starting and poor idle. The fact that it would run on all 6 ruled out a lot of potential problems ( pickups, spark plugs, ignition coils, CDi, etc). However, I did test and change all those parts. I even had a 2nd New stator, but problem was the same.
THE SOLUTION: On a hunch, I reversed connected on of the charge coils (swapped wires 1 and 3). WOW! It runs normally! Finally, after 2 years! Turns out that the NEW Jetunit stators are put together wrong. The two charge coils are out of phase with each other. Instead of adding their voltages, they are subtracting. The charge coils put out AC voltage (probably like 50v and 100V). The engine has been running strong, starting easily, and idling smooth for over a week now. I should add that originally I had a bad stator (OEM), and as I recall, it ran, but poorly. One of the charge coils has failed. So, a GOOD new stator would have fixed the problem, but instead it cost me over $1,000 in unneeded parts, and MANY hours frustration and wasted time.
There is a 50/50 chance that the new Jetunit (Chinese) stator will actually be good (in phase). Not all stators have 2 charge coils, but hopefully this advice can help someone else with a similar problem.
See my original posts here: https://www.thehulltruth.com/boatin...a-200hp-2-stroke-no-spark-port-cylinders.html , and here: https://www.marineengine.com/boat-forum/threads/1989-yamaha-200hp-no-spark-on-port-bank.479827/
It turns out that the problem was due to factory defect on "Jetunit" brand stators. The stators are simple - they have 3 coils (circuits). One gives the voltage for charging the battery. The other two feed the CDI ignition spark (charge coils). There is a high rpm, and a low rpm, charge coil. Each is simply a coil of wire, and the flywheel magnets pass by them and generate voltage for the CDI. So, there are four color-coded wires (two for each charge coil). These wires attach to the CDI box at terminals 1-3 and 2-4. You can test the stator by measuring the resistance of each coil. In my case, the new stator tested as "good". I found eventually that disconnecting either charge coil resulted in the engine running on all 6 cylinders, but with poor high rpm performance, or hard starting and poor idle (depending on which charge coil was disconnected). So, for over a year, I ran with just one coil and suffered with the hard starting and poor idle. The fact that it would run on all 6 ruled out a lot of potential problems ( pickups, spark plugs, ignition coils, CDi, etc). However, I did test and change all those parts. I even had a 2nd New stator, but problem was the same.
THE SOLUTION: On a hunch, I reversed connected on of the charge coils (swapped wires 1 and 3). WOW! It runs normally! Finally, after 2 years! Turns out that the NEW Jetunit stators are put together wrong. The two charge coils are out of phase with each other. Instead of adding their voltages, they are subtracting. The charge coils put out AC voltage (probably like 50v and 100V). The engine has been running strong, starting easily, and idling smooth for over a week now. I should add that originally I had a bad stator (OEM), and as I recall, it ran, but poorly. One of the charge coils has failed. So, a GOOD new stator would have fixed the problem, but instead it cost me over $1,000 in unneeded parts, and MANY hours frustration and wasted time.
There is a 50/50 chance that the new Jetunit (Chinese) stator will actually be good (in phase). Not all stators have 2 charge coils, but hopefully this advice can help someone else with a similar problem.