Mercury 90hp 2 stroke jumping tach and drops out at wot

[Xjclint]

Have a 2000 90hp 2 stroke 3cyl that had the same symptoms last year.

Replaced the coils, fuel pump rebuild, spark plugs, cleaned carbs, and replaced the stator (which fixed it for the past 5 months). Compression is 120, 120, 100. A little low on one but runs fine throughout range.

Took the boat out this weekend and had no issues at all running over 6 hours and 30 miles. Come this week, running the boat at 4500 rpm for 15 minutes and the tach started to bounce around then the motor cut out. Started right back up but then wouldn’t go beyond 3k rpm. I cut it back off and 10 mins later it went back up to 4000 for 10 mins to get me back.

almost seems like it’s a limp mode but I know these old engines don’t have that. The block is also not getting very hot making me think it’s not an overheat. My thought is it Hass to be electrical because it only happens once the engine runs for an extended period at higher RPMs. Bouncing tack is also some indication that there’s an electrical issue. Any thoughts about next steps?

 

[Texasmark]

I think Faztbullet has answered a question of this sort and pointed to the Stator being bad....under the flywheel. If he doesn't catch this post, ping him........Open a new question with the title his handle.

 

[Xjclint]

Replacing the stator last year fixed the problem but it came back this season quickly. The powerpack was new as of last year but maybe there something wrong with the regulator, rectifier, or trigger. It’s kind of hard to test because it only happens after extended use on the water.

 

[Xjclint]

I think the switchbox or the regulator might have been contributing to the stator failure. Can anyone explain to me why this diagram has two different regulators and a separate rectifier? If I wanted to move towards a combined regulator/rectifier from a newer model is there a viable option? It looks like I have the regulator on the left which has two yellow wires and one red wire and then the small rectifier that’s diamond shaped that has three connections, It basically bridges the yellow wires from the stater to the regulator and then there’s one terminal for the tach. Figure I can replace the switch box and the regulator cheaply enough.

 

[Texasmark]

My manual, for 1998 and newer 3 and 4 cyl 2 strokers 75-125 hp shows a 9 Amp reg-rect for the Black stator and a 16 Amp reg-rect for the red stator. So, look up under your flywheel and if you see black you are at 9 and if you see red you are at 16.

The diagram you are posting is not for the 1998 and later engines. There is no switchbox. The engine uses CDI modules that do the switching and high voltage generation directly from stator triggers and power windings.

 

[Xjclint]

Well this is what makes it fun. My serial says it’s a 2000 but it is rigged like an older Mariner inside. 3 coils, switch box, rectifier, 3 wire regulator above the air box. I’m wondering if the inside or outside was swapped at some point.

When I got the engine, it had a black stator. I replaced the stator last year with a 9amp. Totally fixed the issues for 20hrs. Similar issues started happening again this year.

My current plan of attack is to replace the stator, trigger, switch box, and then regulator/rectifier set up with a more modern combo unit. Need to drill out the ignition plate to fit the regulator but otherwise it should all work.

 

[Texasmark]

Well this is what makes it fun. My serial says it’s a 2000 but it is rigged like an older Mariner inside. 3 coils, switch box, rectifier, 3 wire regulator above the air box. I’m wondering if the inside or outside was swapped at some point.

When I got the engine, it had a black stator. I replaced the stator last year with a 9amp. Totally fixed the issues for 20hrs. Similar issues started happening again this year.

My current plan of attack is to replace the stator, trigger, switch box, and then regulator/rectifier set up with a more modern combo unit. Need to drill out the ignition plate to fit the regulator but otherwise it should all work.

If your rect-reg. doesn't come with a black ground wire, the aluminum module itself is ground which could be made with/through a mounting screw...need to ensure it gets a solid path back to battery -.

 

[Xjclint]

Replaced most of the electric and it's good now. Bad rectifier killed two stators.