More 1977 850 Merc problems

[Bluewater84]

so ive cleaned the carbs, cleaned the fuel filter screen, fresh gas in a clean tank, fresh starter. It ran on the first try after sitting a while. Then nothing. Good compression, flow to the carbs, but no kick. I haven’t replaced the spark plugs but will tomorrow. Wondering why it cranked after sitting for years and then nothing. Any ideas? Thanks!

 

[Chris1956]

Well, you need compression, fuel and spark to make her run. You say compression is good, so it is likely one of the others.

If you crank her with the plugs out, you should see fuel mist out the plug holes. Also a good time to check for spark, using a spark tester or timing light.

If no spark... You will have a single switchbox, which if it fails, will kill the spark. Also check the wiring. If the orange wire is grounded anywhere, it will kill the spark.

The other "spark killers" are shorted rectifier, malfunctioning ign switch, ign killer lanyard (not original), failed mercury switch.

 

[Bluewater84]

Yeah I’ve been doing some research and some are saying it could be stator/switchbox issues. Can I test this with a multimeter? Do I need to check for ohms or voltage? Headed out to check for spark right now.

 

[Bluewater84]

I checked the rectifier on ohms and am getting a 1 with I’m assuming is infinity. Is this the right reading or should I have some resistance?

 

[Chris1956]

A rectifier like you have consists of 4 diodes, arranged in a bridge. Google "bridge rectifier" for a picture. Rectifier diodes should test shorted in one direction, and open in the other direction.

 

[Bluewater84]

Ok. So after some more research and talking to a local boat mechanic he is saying that it may be the trigger. I tested for spark with a spark checker and got 0 on all 4. Is there a proper way to test the trigger while it is still on the motor or do I have to take it off to test it? I have found some videos online for 115 but none on 85 and most were off of the motor. After I find out if the trigger needs to be replaced, I’ll obviiusky have to pull the flywheel off but I don’t want to mess up the timing. Thanks!

 

[Bluewater84]

After looking even further I’ve found a suspect wire (white/black) that may need some repairing. According to the wiring diagram I found the orange wire (mine is orange and black) is supposed to come from the switchbox and split off to a mercury switch? I’ve looked all over my motor and can’t seem to find said switch. Also the orange/black kill switch is going directly into my throttle. Also the rectifier wires are almost toast so going to repair that as well and give it another shot. I’d still like to try the trigger with a multimeter while it’s still on the motor but not sure what settin or where to put the lead at.

 

[Chris1956]

The wire colors you cite are not standard for a 1977 Merc. You might look on the maxrules web site for a matching wire diagram.

Sometimes the mercury switches are removed. They look like a condenser, but in blue plastic. They are normally mounted on the cowling support, near the carb throats.

 

[Mercurylips]

The part # is 58124A19. The part looks like a 1 1/2 " Long by 3/4" thick silver cylinder wit wiring coming out of the back. Should be imaged in a schematic listing your flywheel, Stator and switchbox. Mine was located attached to the front housing by my starter and close to the carbs.I do have a different motor. Just from the same year.

 

[Bluewater84]

Can somebody send me the proper links on max rules ? I’ve found one or two that look right but I just want to make sure. Had to take the main wiring harness out of the motor. Not a single wire was in good shape. Thanks!

 

[Texasmark]

Fuel or spark.

Fuel, you had a piece of crud (varnish...dried up fuel) clog a fuel passage but the most susceptible place would be a carb but that engine (I bought one new the mid 70's) has two so one should have allowed you to at least have a sputter.

Quick test is take some Sea Foam, remove the cover to the air box accessing the carb air intakes and shoot both carbs a couple of strokes. If it hits or runs and stops, fuel problems....go through the whole shebang including replacing ALL hoses including line from tank to engine with new Quicksilver brand squeeze bulb....get the arrow pointing toward the engine.

Electrical. Chris is on it. Been too long remembering what mine had.

 

[Bluewater84]

Well....again I’m my learning process I’ve found rewiring the harness might be a bit difficult seeing is how the wires are basically fused into the main plug. Or can I bypass this? I was going to just re wire with fresh wiring but it looks like I’m going to have to buy a whole new harness. Does this sound about right? Lol

 

[merc850]

If it really is a 1977 this wiring diagram is it, the rectifier only charges the battery the ignition is fired by the stator/trigger assembly and this requires the motor to turn over quickly; you can even run it with the harness disconnected. I would check the ground wires at the switchbox and coils.

 

[Bluewater84]

Yep! That’s it. The old harness was so corroded the wires were literally falling out of the harness end. Which is crazy because it fired up the first couple of times great. I don’t know how it even had enough wire to do it. Anyways. Looks like I’m gonna have to drop a Benjamin on a new harness. Unless somebody out there knows where I can get a good used one or somebody has one laying around they can come off of.

 

[Mercurylips]

Used one? You will probably get what you have......... A problem. A new harness is what is needed. Replaced everything bad on mine and there was much bad wiring. Replaced the stator and it was also bad.

 

[racerone]

The plug in feature is for convenience.------Nothing to stop you from making up a terminal board to mount in the engine.----Red wire to red then blue to blue etc, etc.

 

[Chris1956]

The engine harnesses are well available on the web. So look for a good price.