View Full Version : 70HP 2 Stroke 3 Cylinder - Running rough after stator install

08-30-2019, 07:22 AM
Hey everybody,
First time posting, and new to boating so here goes!

I've got a Mercury 70HP 2 Stroke 3 Cylinder motor from the late 70s/early80s and the thing ran great. One day, it was having trouble starting. I did some tests for compression, spark and fuel and everything *seemed* to be OK. Fast forward and it turns out the spark was too weak which is why it was only starting intermittently at best. I took off the flywheel cover only to uncover the stator wires were completed rotted. I replaced the stator, and now she finally coughs again. The problem is when I installed the stator, I had to install it backwards (180 degrees) off because the wires for the new stator were way too short. Instead of cutting and splicing, I installed it backwards just to see whether I would get a nice strong spark again. Motor will now start up, but it almost sounds as if the timing is off. Now I'm wondering whether I should go back in there, and splice the cables to make them longer in order to install the stator the "correct" way. Can anyone confirm whether installing the stator in a different direction could cause a timing issue? I'm 100% sure I didn't mess with the timing because I didn't have to use a flywheel puller to remove the flywheel. I have the red flywheel cover with 6 or 8 bolts that can be removed in order to gain access.

Here's the problem.... when I was diagnosing the boat, I initially had spark, but in fact it was very weak because of the stator failing. So I thought it would be best to do a carb clean since this was a boat motor that was new to me and I was having starting issues. Carbs have been rebuilt although the carbs weren't really all dirty to begin with.

Now I'm wondering what to do first. Should I a) Keep fiddling with the carbs because I may have done something wrong or b) Open up the flywheel, extend the stator wires, and reinstall the stator as it was when I removed it?

Thanks in advance for your help :)

08-30-2019, 11:01 AM
I've been told by CDI that the stator CAN be moved to another location, but it shouldn't be. (??) I hate to splice as well, but I'd do it in this case.

First, get spark back and then tackle the carb problems.


08-30-2019, 11:28 AM
Thanks for the reply. I've seen mixed information about the stator. I think you're right. I'll start by splicing and putting the stator back to the same way it was from the factory. At least I don't have to worry about another variable. Should make troubleshooting much easier.

08-30-2019, 01:48 PM
If you have to ever get another stator, here is a pic of my new CDI compared to the stock stator; the CDI stator and its leads are on the right. I made sure to mark the location of the old stator so that I got the new one the same.

09-03-2019, 07:18 AM
Thanks for the feedback. I think I know what I did wrong. I have 8 bolts around the flywheel and instead of using the puller, I decided to unscrew the bolts and remove the flywheel to access the trigger. Where I messed up was *not* marking the orientation of the flywheel before removing it..... so I believe the timing is off which is why I'm having trouble getting the motor to run. I'll have to get cylinder one at TDC and then attempt putting the flywheel cover back on correctly. To add to this, the starter solenoid or starter is now acting up. Going to have to fix that before I continue troubleshooting. I made a little switch and connected to the stater solenoid...same reaction as using the key in the ignition so I don't think I have a wiring problem. New solenoid is on the way.

09-03-2019, 09:26 AM
Keep us up on your progress.