trouble shooting a 1978 90 hp ,modle 900

Was wondering where to start ,turn key nothing ,pushin and turn key ,you can here the choke kick in,i am thinking starter hook pos and neg of starter and touch to the battey nothing help?

Re: trouble shooting a 1978 90 hp ,modle 900

the (-) side of the battery, usually black lead, connects to the engine block and a wire from the starter does also. That completes the ground circuit. Power comes from the (+) terminal on the battery, usually red wire and terminates at one large terminal on the starting solenoid (switch). The other side of the switch is the other large terminal and it goes, via a red wire to the other wire from the starter. To spin the starter (if all is well) just close the switch, or jump around the big terminals on the solenoid with a pair of common pliers....crude, but it tells you in a heartbeat that everything but closing the solenoid works.

On the solenoid are 2 small terminals. One goes to ground and the other to the ignition switch and when it is in the "Start" position is sends 12v to the solenoid and it energizes closing the high current contacts and spinning your starter.

That's how it works. So come back with which part of how it works is not working for you....and ensure you have a well charged battery with good clean contacts, primarily inside where the metals are in contact with each other.

Mark

Re: trouble shooting a 1978 90 hp ,modle 900

Turn the key and wiggle the throttle handle. If the starter spins, you probably have a neutral interlock switch issue.

Re: trouble shooting a 1978 90 hp ,modle 900

I took a wire and attached it to the + stud then wire to the ground ,and touched directly to battery ,nothing happened ,shouldnt that of engaged the stater?

Re: trouble shooting a 1978 90 hp ,modle 900

Let try this again ,ok i put a red wire on the + stud of the starter then a black wire to the - of the starter then touch them to the fully charged battery ,shouldnt that of engaged the starter,

Re: trouble shooting a 1978 90 hp ,modle 900

Yes. Did it spark when you attached the second wire? What gauge were your test wires....large enough to carry 100+ amps?

Can you rotate the bendix and rotate the starter shaft with your fingers.....looking for a frozen armature/shaft?

Mark

Re: trouble shooting a 1978 90 hp ,modle 900

On that starter, there should be a black thick wire bolted to the top of the starter and to the top cowl support. The only stud on the starter is the positive connection. Is that what you are seeing?

Re: trouble shooting a 1978 90 hp ,modle 900

cant turn it with your fingers or wrench

Re: trouble shooting a 1978 90 hp ,modle 900

yes the + stud is what i put to the hot ,and neg bolt is what i put the othere wire and touched to neg and not a thing happens

Re: trouble shooting a 1978 90 hp ,modle 900

been there done that. make sure your battery connections are 100% my prob was there was power and connected and clean but positive was crappy 1 1/2 inch from the pos connector. so I cut it and put a new end on it and viola now cranks all the time. maybe same problem who knows. my engine has other problems

Re: trouble shooting a 1978 90 hp ,modle 900

texas ,no spark or anything,maybr bigger wire ,used 14 ga

Re: trouble shooting a 1978 90 hp ,modle 900

Sounds like your starter is open. It would have started to spin, if it was good, even with that 14 ga wire. Of course the wire likely would have melted.

Time to pull the starter and have it tested, or open it up and inspect brushes, armature, commutator and magnets.

Re: trouble shooting a 1978 90 hp ,modle 900

thanks to all ,i will check the manual ,what do you usally look for when you tear down the starter ?

Re: trouble shooting a 1978 90 hp ,modle 900

They are a bit tricky to ohm out, since the windings on the armature can be connected together. Put an ohmmeter on the commutator and check each piece of copper for short to the steel post of the armature. Short is bad. Usually you will see bad or cracked brushes or a dirty commutator. Clean up commutator with extra fine sandpaper. Check brush springs. sometimes they melt or get weak.

Those Merc starters can have 4 vertical brushes. These are a real PIA to re install. Cut a slot in a piece of cardboard or thin metal. Put the cardboard or metal over the brushes which you have hand seated. Hold them in their seats while you reassemble the starter. Now pull hte cardboard or metal out as you push the case closed. The brushes will be in their holders, if you do it right.

Merc has a special u-shaped metal tool to make this easier.

Re: trouble shooting a 1978 90 hp ,modle 900

got the starter off ,sprayed shaft with wd 40 got it broke loose ,going to tear it apart after supper not sure what i will find but dont think it will be good, found out the covers have been off the motor all last winter and all year,why would you leave it all out in the open ,thats just being lazy ,no telling what all will need rebuilt

Re: trouble shooting a 1978 90 hp ,modle 900

rkerr said:

got the starter off ,sprayed shaft with wd 40 got it broke loose ,going to tear it apart after supper not sure what i will find but dont think it will be good, found out the covers have been off the motor all last winter and all year,why would you leave it all out in the open ,thats just being lazy ,no telling what all will need rebuilt

Click to expand...

I think you just said that the shaft was stuck and that you now have it freed. Well sir that is a different story. Now your system should work if all your large wire (high current) wire connections are bright-shiny and tight...inside and out.

On your 14 ga test wire. Look at the wires going to the starter and at your 14 ga test wire. You tell me if you think it would carry adequate current...14 AWG is usually fused with a 15 amp fuse to keep the normal Nomex insulation from melting. We're talking about 100 amps to start and more if it has a locked rotor which you seem to have had.

Thennnnnn when you have done all the above cleanup and all, if it still doesn't want to comply, then you may have cooked the contacts inside the solenoid and another is required.....to have contacts that will cover the 100+ amps needed for starting.

Mark

Re: trouble shooting a 1978 90 hp ,modle 900

everything is rust ,can you soak it in anything to get rust off all the copper wires

Re: trouble shooting a 1978 90 hp ,modle 900

Remove all the wiring connecting the battery to the engine, including wiring to ground, the solenoid high current in/out terminals, the starter terminals and all terminals in the loop from battery + through the starter, out the other side and back to battery (-) via the engine block. One terminal at a time is ok then you won't loose track of what goes where. Medium to fine steel wool will polish up the tin plated copper terminals and a wire brush the 3/8" studs.

On the lead battery terminals, get a battery brush (auto parts store) and clean both the battery terminals (push the female brush down on the terminal and twist half a dozen times). Use the male end to clean up the mating connector on the cable. Where the wire is crimped to a connector this may be a good contact and may not. Only thing you can do there is to replace the whole cable which may not be a bad idea with what you said about rust. Auto parts stores/WWorld has them.

When finished spraying with Brake Parts Cleaner (auto parts store) will blow off all the residue and evaporate in a couple of minutes. A light coating of grease will help to protect the connections when finished.

I am assuming that you did dislodge the stuck rotor and cleaning up the wiring should restore your performance. Wouldn't hurt to put some oil on the Bendix (spring loaded gear on the starter shaft) and run it up and down the shaft a couple of times so that when you get the starter to spinning it will jump up and engage the flywheel and come back to rest when released.

Mark

Re: trouble shooting a 1978 90 hp ,modle 900

Mark, Does that brake cleaner disolve varnish, like carb cleaner does? If so it will ruin the starter.

Re: trouble shooting a 1978 90 hp ,modle 900

thats what i was worried about