'78 800 won't start with new trigger, stator and internal harness

[1970Thunderbird]

Hello all,

A few weeks ago, I had my boat out with my new-to-me Mercury. It cranked and ran well, but didn't seem to have any top-end power. When I got back home, I gave it a look over and noticed that almost all the wiring was shot. I was amazed it even ran.

I ordered a new trigger, stator and internal harness and replaced them. Now, however, the darn thing won't run.

I have spark on all four cylinders.
I've tried running without the kill switch wire attached, but no luck.
Tried running without the yellow wires attached to the rectifier, but no luck.
Tried bypassing both the kill switch and rectifier, but no luck.

I've noticed the a wizened member on here stating the position of the stator is irrelevant. I did, however, do my best to reinstall it in the same position as the original.

I suspect I have a timing problem. Do you agree? Or could it be something I'm overlooking?

For the most part, the motor just spins and spins. It will occasionally catch and attempt to run, but dies within a few seconds.

Thanks for your help

 

[Chris1956]

Re: '78 800 won't start with new trigger, stator and internal harness

Sounds like you may have the trigger set incorrectly. Put a timing light on her and see where she fires.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Chris,

That was my initial thought. I also wanted to do a more indepth check of spark, and I discovered my top two cylinders will arc across a 20mm gap, while my number 3 cylinder will arc across a 10mm gap. Number 4 doesn't seem to be firing at all.

This'll be my first time using a timing light. Any tips? Also, how do I adjust the trigger?

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Chris,

I forgot to add this: how can I adjust the timing if the engine won't run? My understanding is that the engine needs to be running in order to properly adjust the timing.

Thanks so much.

 

[Chris1956]

Re: '78 800 won't start with new trigger, stator and internal harness

The engine does not nee to be running to test and set the spark advance. Remove spark plugs 2-3-4 and install them into their wires. Now tape them together so their bases touch, and then connect their bases to the block. Put timing light on top cylinder, and crank motor. Aim timing light at timingpointer and when light flashes, read timing setting. I am not sure of the timing specs for your motor, however, using this method you can test and set idle pickup timing and max timing which is all you will need to set.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Chris,

Thanks for the advice. I ordered a timing light and remote starter (in the event I can't find a monkey to turn the key). I have a Seloc manual and it suggests 2 degrees BTDC - 2 degrees ATDC for primary pickup. It says 27 degrees BTDC for max timing.

I'm hoping to put it in the water tank and give it a shot tomorrow when the timing light comes in. If you can think of anything I should know before starting this project, please let me know. I appreciate all the help and will either be back with more questions or the good news that everything works.

Thanks!

 

[Chris1956]

Re: '78 800 won't start with new trigger, stator and internal harness

You can use a simple clip lead to energize the starter solenoid. No monkey is required. Jumper the heavy red lead on the starter solenoid to the yellow lead on the starter solenoid, and the motor willl crank. Remove the prop for safety, as it is easiest to set max spark advance when motor is in gear. The propshaft will spin so keep your feet and all the monkeys away. It is best if you can set timing while you are in the boat, for safety.

I would recommend a 23* BTDC max advance, vs the 27* called for. Today's fuels are not as good as when that motor was made.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

I was having a thought. What actually causes the trigger to fire? I ask because I want to make sure I have everything back together properly. I have a large washer that I assume went between the main nut and the flywheel, so I placed it there. I seem to recall the manual mentioning a magnet beneath the flywheel (not the ones embedded in it), but never saw one.

So it appears as though my course of action is to set the primary pickup, and once that's done and the motor's running, set the maximum timing. Is that correct? I should be able to be in the boat, but my trailer has a tendency to tip backwards if not hitched. Looks like I'll need to weigh down the tongue. My biggest concern is that the motor's gonna fling out all the water in my test tank at full throttle. Perhaps that won't be an issue with the prop removed. The engine won't cool properly on muffs.

 

[matth121]

Re: '78 800 won't start with new trigger, stator and internal harness

the reason your removing the plugs and watching your feet is because you'll be doing this on dry land, without the motor running. just cranking, since the plugs you removed arent in, the engine wont run, just turn over with the starter. Hope this clears it up for you. I just had my flywheel off today, mines smaller of course, 1982 25HP, but i had 2 magnets on either side for the stator and one in the center on the flywheel, for the trigger- this center magnet slides down over the crankshaft on mine and is part of the flywheel, cant see it moving or coming off. Good luck

and dont forget to remove the prop. that could hurt.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

My main concern is that the center magnet of which you speak may be missing. Very doubtful, but I did have a thick, circular piece of metal that I took for a washer. I wonder if it should have gone beneath the flywheel rather than between it and the main nut.

I intend to remove the prop and mount the motor in a large basin we have at work. It'll be large enough to amply run the motor, even up to WOT. I know I may not need it for setting the timing, but I would like to run it all out once I do get it set, just to make sure there aren't any other gremlins hiding in there. Hate to find them on the lake.

 

[matth121]

Re: '78 800 won't start with new trigger, stator and internal harness

im still a noob here and to this stuff, but i already know for sure.....DONT RUN YOUR ENGINE AT WOT IN NEUTRAL(with no prop it's just like being in neutral). If the center magnet is gone- you'll never have spark. It tells the engine when to fire(trigger actually but that uses the magnet). I'd reccomend setting your timing on dry land without engine running, as the procedure dictates, then go for a test run. If your worried, stay close to shore, lol. good luck

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Good news! My timing light came in today, so I put the motor in a large basin and checked the timing. Way off; about 8-10 ATDC for primary pickup. I got that corrected and the motor cranked and got it idling. Which brings me to yet another question: What are these supposed to idle at? I had mine dialed down to about 900 rpm, and it seemed fine. I think I need to do some more adjusting, as the only way I can get the controls that far back is by pushing on the levers in the engine. Shouldn't be too difficult, though.

Also, how do I go about testing the engine for maximum spark at full throttle? I can't test the engine in the basin with the prop spinning, as it forces all the water out, causing a giant mess. Do I have to wait till I'm on the lake to do so? Seems like a big hassle, plus I may lose tools overboard. I did manage to get the engine up to about 5,200-5,300 rpm briefly using the warm-up bar on the controls.

Which brings me to yet another question, and I apologize if this is the incorrect forum, but shouldn't my main throttle control operate as both a forward/neutral/reverse selector, as well as a throttle? Because I don't think I can get into full throttle using the main control. The warm-up bar, however, takes it through the full range of power.

One last thing: the orange wire on the internal harness is to kill the motor with the switch, correct? The switch no longer kills the engine. If I want to shut off the motor, I have to starve it of fuel. Any thoughts?

Thanks all.

 

[PHE]

Re: '78 800 won't start with new trigger, stator and internal harness

You set the max advance the same as the idle advance, without the motor running. Simply advance the throttle to WOT and read the timing using the method Chris described.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Ah, sounds simple enough!

Any thoughts about the kill switch or throttle bar?

 

[Chris1956]

Re: '78 800 won't start with new trigger, stator and internal harness

gee, The large handle on the control should be gearshift and throttle from idle to WOT. The warm up lever should advance the throttle only a little but for cold start. The kill switch needs to conect to ground to kill the motor. The key switch also connects the orange wire to ground to kill the ign.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Chris,

As far as the throttle is concerned, the warm up bar will take it all the way to about 5,500 rpm. I'm not certain about the main lever, as I haven't taken it to the lake yet.

I am completely baffled by my switch problem. All the wires show a good connection. The switch is working properly, according to my ohm meter. And the switchblock is functioning properly as well.

I ran a jumper wire from the kill post. I had the engine running and touched the jumper to ground. It killed the engine.

 

[Chris1956]

Re: '78 800 won't start with new trigger, stator and internal harness

Maybe you have a break in the killer wire between the switchbox and the ign key? The quick disconnect plug is a likely culprit.

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Chris,

That was my initial thought, so I tested the ohms from the wire (disconnected) at the switch box, all the way up to where it's soldered into the key, while connected through the quick disconnect. Did this for both the kill wire and the ground. Both tested perfectly. And I checked the switch. It, too, checks out. I even put some dielectric grease into the quick disconnect for the kill wire. No dice.

 

[Chris1956]

Re: '78 800 won't start with new trigger, stator and internal harness

Did you test continuity from the origin of the orange wire at the switchbox, up to the key, and back on the ground wire to the motor cowling or neg post of the battery? Maybe the ground wire is broke in the quick disconnect plug? Did you get a dead short to ground?

 

[1970Thunderbird]

Re: '78 800 won't start with new trigger, stator and internal harness

Chris,

The simplest explanation is often the correct one. My switchbox has several wires coming from it that I assumed to be ground wires. Wrong. I connected a jumper from a ground spot on the switchbox to the negative ground on the starter, as I was positive that would ground it.

The key works perfectly know. I also know to never assume. Thanks for all the help. With all the new wiring, the motor cranks on the first try, chokes electrically, runs beautifully, and shuts off when commanded. I'm very much looking forward to really putting it through the paces this weekend.

Thanks so much for all the help. I really appreciate it.