115 four cylinder, switchbox (CDI?) meltdown

[lmuss53]

I have a Mercury 115 four cylinder early oil injected SN 0D106981, that was hard starting and had no power when they tried to get it up on plane, I at first thought it was a carb issue but when I pulled the cover off I saw that the switch box had been real hot and had cooked a lot of potting out and melted it down over the side of the motor. Nothing else looked as if it had been at all hot. The motor still has hot, blue 1/2 inch spark coming from all 4 plug wires, but I am told these boxes have a "high side" that kicks in around 2500 rpm, and that is what has failed.

My questions are as follows:

What did this, can I get a new one and assume it will fix the problem?

Is there more troubleshooting that I have to do, like on stator, other things?

The stator looks fine, none of the tell tale hot spots or melted off insulation you see with failed stators sometimes.

I've ordered the box, even if it is still working I can't imagine it can for long like it is.

Thanks in advance for any replies.

 

[Faztbullet]

That a first generation switchbox and it has a CDI stator already. Check grounds on ignition plate....

 

[lmuss53]

I'm assuming the ignition plate is under the flywheel. Pull the flywheel and check the grounds? Is it the stator body or are there wires? I can see why that would be important, the stator looks pristene, brand new.

I tried the troubleshooting procedures on the CDI sight. I got no DVA voltage dropoff all through the rpm range to 4500rpm with the prop off, in a tank, in gear, but no real load. I did find that it runs MUCH better with the regulator/rectifier unhooked, I didn't realize how bad it was running until it ran better, The second I unplugged the first yellow wire it smoothed out and the run up to 4k in the tank was much much smoother and stronger.

I could not get a bad reading on any stator output, both on the red/red-white, and blue/blue-white wires going to the melted box and the yellow ones going to the rec/reg, everything read good according to the CDI troubleshooting guide. The voltage from yellow wires to red going to solenoid was under a volt. 850 Mv, is that right? Both were the same and they rose from way low when I hooked them up, CDI didn't give a voltage just said they had to be the same.

All that suggests the stator and reg/rec are ok, but the motor runs better with rec/reg unhooked?

My head hurts.

Thank you sir for the response.

 

[dmoriarty51]

Subscribing, I have a 115 4cylinder that is unhappy with rpm also that things seem to all be checking out on so far.

 

[Faztbullet]

No the ignition plate is the aluminum plate switchbox,rectifier,etc are mounted on...

 

[lmuss53]

OK thanks, checking all connections top to bottom, guy has an industrial battery in it, I will suggest he gets marine specific battery for this, Hot lead on battery was finger tight, gonna get rid of wing nuts , tighten all connections. I will change the regulator, and the meltdown box, I think that and, the cleaned, tightened connections will fix these issues.

Dmoriarity, per the CDI troubleshooting guides, unplug the regulator and see if the midrange miss goes away. If it does do the rest of the troubleshooting and see which of the components is causing the problems. Make sure everything else is ok first, compression test, fuel supply and flow.

 

[lmuss53]

Well it started, idled and sounded much better with the new box and rectifier/regulator, but still has no power. Next will be a test ride with a known good tank and hose, pumping the ball to see if additional pressure gets it going. If it doesn't perk up then the carbs come back off for cleaning. Any further suggestions?