Starter randomly engages while motor is running

[misterpancho]

I have a 2002 Mercury 40 hp 3 cyl / 2 cycle. When revved or running above idle speeds the starter drive gear will randomly raise up and engage the flywheel for brief periods of time (just enough to hear the clank). You can see the drive gear move up and down slowly while the motor is running - it's a very gradual thing and sometimes it moves up far enough to touch the flywheel - it's not a quick, complete movement like when you turn the key.

Another problem I've noticed is that the insulation on one of the yellow wires is pretty severely melted and it seems like it still gets hot so whatever is causing the overheating still needs to be corrected. I'm not sure if this is related to the starter problem or not, but I wanted to mention it.

I would appreciate any thoughts on where to start diagnosing / troubleshooting. I can add a picture of the wire if it would help or a video of the starter moving. The motor is new to me so assume any and all negligence is possible.

 

[jimmbo]

You need to determine if the bendix is rising from the starter motor raising it or from a weak spring on the bendix. You need to determine if any current is going to the starter when it shouldn't, an ammeter that fits around the cable between the starter and solenoid will revel that.
Melted insulation means a wire is carrying far more current than it is rated for, Shorts to ground or internal shorts in coils/solenoids can cause that. You need to get the wiring diagram for your engine and go over that circuit that is trying to be a fusible link

Video of the bendix movement would be nice.

 

[misterpancho]

Thanks, that's helpful. I've got the lower unit off right now - once I'm done with that I'll look into those and put up a video.

 

[misterpancho]

I'm waiting on parts to finish up the lower unit but I got a wiring diagram. Regarding the burnt insulation, there are two yellow wires on this model that run from the regulator to the strator. The burnt one is the top one and it burned the insulation over the blade connectors closest to the regulator - nothing appears melted anywhere else.

Looking at the wiring diagram I'm starting to feel that the starter issue and the melted insulation are probably unrelated. I'll test the amperage between the solenoid and the start motor like you suggested, and I'll start a new thread regarding the melted wire if I can't sort it out.

 

[tommarvin]

Time to start testing ignition parts with a multi meter or something better. for regulator/rectifier, you may have a trigger to test on a two stroke and the parts connected to the burnt yellow wire.
Interesting , the starter works great its only a 2002, but creeps up to flywheel.
Do you have a malfunction indicator light to read error codes. Or anything to read error codes.
Do you have a factory service manual to diagnose fix your motor, it complicated.
If all else fails buy a starter on ebay for 40-45 bucks,and shrink tube over the burnt wire.

 

[misterpancho]

So making progress on this motor! I thought I was going to have to go through the carbs but I changed the fuel filter and it idles and starts great now. Also had a really weak stream from the tell tale and after a new impeller and a little compressed air it's pumping good water now. This is my last gremlin!

Have a look at this video, basically when you bump the throttle above idle the starter engages. This is some weird stuff:

https://www.youtube.com/watch?v=LH7LbgSNfA8&feature=youtu.be

 

[misterpancho]

Also I let it idle of for about 10 minutes just now and the burnt wires didn't feel hot at all. I'd really like to try to diagnose the problem instead of randomly throwing parts at it.

 

[jimmbo]

Check inside the control box for any contact between the throttle linkage and ignition switch wires, and on the engine for any wire/linkage contact

 

[Fed]

The connector needs to be cut out & replaced (both halves).

The starter motor appears to be energizing rather than the bendix gradually creeping up, put a voltmeter between the positive starter motor terminal & ground to see if it's getting unwanted voltage when it does it's thing.

 

[misterpancho]

yes I agree it is definitely energized. before when the motor idled very rough and it would creep up, but now that I've got the idle sorted out it jumps up, which to me suggests some relationship between RPMs and the starter behavior.

I'll check for any problems with the connections near the key, but it's a tiller motor and the key is over on the side of the boat so that rules out the throttle linkage scenario I believe.

I'll do some checking with the the voltmeter tomorrow. You would expect no current going to the starter when the key isn't being turned, correct?

 

[Fed]

You would expect no current going to the starter when the key isn't being turned, correct?

Correct, but check for voltage as I doubt you have a DC clamp meter.
Next step after that would be checking for unwanted voltage at the starter motor solenoid across the 2 small terminals.

 

[misterpancho]

Weirdest thing, I took a few of the connections off the solenoid to do some tests. After connecting them back up and running the motor it stopped doing it altogether. The only thing i can think of is some kind of residue or something might have been allowing a connection to be made between the main +/- posts on the solenoid.

??????