Yamaha F80 rectifier suspected overheating, smoke, 30A fuse opens, engine stops

[BoatAddicti0n]

My engine, Yamaha F80 year 2002, carburetor, total 167 hours, has been running like a dream...before.

The problem I have at the moment is that the motor stopped to run suddenly after about 5 minutes in idle, first run of the day, showing smoke close to the electric distribution box in the front of the engine. Actually the engine not only stops, but start motor and trim/tilt would not show any sign of life any longer.

I found an open 3O A fuse. One end if this fuse is connected to the voltage rectifier/regulator (red cable), the other end to the start motor solenoid, and to both power trim/tilt relays (see diagram picture). No signs of burned cables around the area. But close to the back of the regulator/rectifier, the motor block is sooty (well, the whole motor block is very clean, but not there). In addition, the back of the voltage regulator/rectifier seems rough when I touch it and I had the impression it smells smoke (other Yamaha rectifiers I have seen before are smooth on the back). I could not remove it yet, would need to remove the intake silencer and probably the throttle lever...will do it tomorrow. Anyway, I did not see which was the source of the smoke and cannot be conclusive, so far.

I did replace the opened 30A fuse for a 20A and ran idle for short time, less than a minute, but the rectifier/regulator heats (what seems a bit too much to me).

What was done before the problem and that could have triggered it:
I have installed a battery main switch (ON/OFF type, one battery). The installation is pretty simple as you know, the short battery-to-switch cable is brand new and tested good. The connections were checked and double-checked good. But when I first run the engine idle after the installation, I did something that might have triggered the problem: I have turned off the battery while running idle, the engine died directly, started fine after switching on the battery, but finally stopped suddenly after about 5 minutes running idle as described in the beginning of my post.

Maybe someone knows that switching off the battery when the engine is running blows the rectifier (what I find a bit low robustness but, well, at this point I would be glad to buy the right part and have it running as before again)

I would really appreciate to have advise on the way forward of my troubleshooting, how to identify the root cause, if it is possible that relay or any other things are the cause, how to test rectifier/regulator, and so on...

Thanks a lot /B.A.

 

[boscoe99]

Remove the rectifier /regulator and inspect it carefully for any signs of heat distress. Carefully check the back side of the unit.

The F80/F100 rectifier regulators are known to be problematic. If you saw smoke it is damaged. Remove the CDI which sits above the R/R. Hopefully it also has not been damaged from heat.

I suspect that your R/R is toast. Not uncommon as I have noted.

If and when replacing any parts make sure that all electrical connections are clean and properly secured.

 

[99yam40]

In other words loose battery connections have been known to cause RR failures.
May not be what caused yours, but need to check all to make sure

 

[BoatAddicti0n]

Not much to say, a 2 inches ugly scar on the back side, melted cables isolation, the RR was actually fried.
Picture failing to upload...

Even in that condition, the RR could operate trim/tilt and start/run the motor (what I did yesterday after the smoke, a few seconds test)
In addition, the CDI was not affected as it seems externally and all cables seem good, except the ones in the RR.

As 99yam40 mentioned loose battery connections have been known to cause RR failures, I have very little doubt the root cause was any other in my case.

Would be just replace RR and go or should I check any other stuff ?

Of course battery connection is now on top of the boat check list..

Thanks for the feedback!