1973 85 hp Merc,, Lost spark while idleing

[nomorefords]

New fuel pump kit.
motor is getting fuel just fine.
Wont so much as pop with starting fluid.
My wife and i were trolling almost to boat launch ( thank the Lord! )
The motor shut off as if I'd turned the key to off
Plugs are clean and brand new

what would be the most likely problem?
is there a part i can remove and have tested?
What would it look like? what color wires would it have going to it?

I have two childern serving you and me in the armed services they will both be home soon for a family reunion, I promised a running boat when they come home.
We live on a very limited income and cant afford the big bucks a marine shop demands. we may however afford a part or two.
Ive gotten help from you fine folks before, and look forward to your help once more.

Thanks for reading!!

Doug

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

I just read another post about a mercury switch on a 1974 model twas a 65 hp though,,and it was the guys problem,, I wonder if mine has one and where it might be

 

[Fuzzytbay]

Re: 1973 85 hp Merc,, Lost spark while idleing

the mercury switch is mounted on the power head, it could also be the kill wire to the switch box is grounding out. If you post the serial number it would help to pinpoint out wireing colours too.

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

Thanks fuzzy

# is 3746584 is the power head the box directly behind the face plate in front of the carbs? if so it has 4 wires going in,,,3 going out,, green on top brown 2nd,,green 3rd,, and white on bottom,,, also wires from plug going to a smaller box to left of plug with 3 wires going in,, red in center,,2 browns on yellow contacts going out and under the flywheel

Thanks again fuzz

 

[usskydvr]

Re: 1973 85 hp Merc,, Lost spark while idleing

That's not the powerhead, that's the switchbox. ( It takes signals from the distributor and charges up and fires the coil). On the side of the switchbox that has only three wires,
they should be
Top - Black
Middle - White
Bottom - Brown.
the Brown goes two places. One to the distributor the other to the msercury switch. ( This switch prevents the motor from running when it is tilted up too far). If you disconnect the wire that goes to the mercury switch and your motor now runs then the switch is bad and needs to be replaced.
The powerhead is the motor block.

 

[usskydvr]

Re: 1973 85 hp Merc,, Lost spark while idleing

Also the small box with the yellow and red wires that go to the flywheel isg the Rectifier. (changes AC from the stator/flywheel assembly to DC to run the engine and charge the battery)

 

[Chris1956]

Re: 1973 85 hp Merc,, Lost spark while idleing

That ign system needs to have +12VDC on the red wire on the switchbox, at all times. The white wire next to the red (non-distributor wire), must have voltage on it when the key is in the run position.

On those old boat and motor harnesses, wires do break..... I had the white wire break at the quick disconnect many years ago, and my motor was newer than yours. I ended up splicing in a new wire, and sealing it with silicone caulk.

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

Thanks for your help fellas

After removing some black tape from a lot of the wiring I found several missing insolation, copper is still in good shape, nothing broken, but i need to replace a few. The white that Cris mentioned is bare from the sillynoid to the quick connect. that to i can take care of. All 3 wires that uss mentioned go into the distributor, I still see no sign of a merc switch. I did notice however a 3/8 dia hole in the side of the dis without a plug of any kind its in the bottom half of the dis. Im sure insects could enter and make homes. are there any concerns in removing the cap for inspection? What should I look for once in there,, anything contacts to be cleaned? any lil springs gonna drop out on me? haha

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

Its my understanding that there are no points on mercs,, is that true?

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

Just noticed,,timing belt is in no way snug,, rather loose fitting,, but not broken, is that the norm ?

could it have jumped out of timing enough not to even backfire?

 

[Chris1956]

Re: 1973 85 hp Merc,, Lost spark while idleing

The hole in the distributor cap was for a plastic fitting that held a screen for ventilation. You might remove and clean up the cap. The rotor is non-removable. The cap has a cost of $100+, so dont break it.

That Merc has a "Hall effect" trigger system, rather than points. You will see the four windows in the timing disk, with teh dist. cap removed.

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

no wasp nest in the dis,,, but plenty of moisture,, contacts dont look to bad but cleaning anyway

Thanks Cris!

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

for my bare wires, I thinly coated with silicone, took oxygen breathing tube, cut to lenth, slit down the center of hose and wraped the wire, then electrical tape. I seperated the wires as well as possible at the quick connect and used a marine sillycone to fill the void between the wires I dont think what i'm doing is a fix for my problem, but it needs to be done.

 

[usskydvr]

Re: 1973 85 hp Merc,, Lost spark while idleing

So when looking at the three wires that go to the Dist, on the terminal with the Brown wire, there should be another wire connected. That would be the wire that goes to the mercury switch. (unless a previous owner took it off)
The timing belt should be snug. You can check the timing (at least close enough to get an idea) by putting the throttle wide open, (so the distributor is rotated all the way against the timing advance stop bumper), removing all the spark plugs, hooking the #1 (top) plug body to gnd, turning the ignition on, rotating the flywheel by hand until you hear the spark, then looking at the marks on the flywheel to see where they are on the timing tape

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

1 took cover off surrounding flywheel and inspected the belt about 1/2 inch play and belt teeth seem to be ok

2 took out all plugs pluged in # 1 cylinder and grounded ,turned on key, full throttle, spun flywheel by hand,,, no spark

3 repaired all wires that were bad

Could I remove the coil wire at the dist,, stick in a test wire or screwdriver and ground it looking for spark?

I dont have a helper so could I turn it over from the silnoid using a screwdriver to cross power to small wire?

 

[Moody Blue]

Re: 1973 85 hp Merc,, Lost spark while idleing

First thing is DON"T pull the wires out of the distributor cap. They are screwed in.

As for the no spark issue, first thing to check is that you have the proper voltages at the right terminals on the switchbox as Chris1956 pointed out earlier. Without that, you will not get spark, and based on the description of your wire condition I would be very suspect of a broken wire somewhere in the controller, harness or engine harness.

 

[Moody Blue]

Re: 1973 85 hp Merc,, Lost spark while idleing

Duplicate post

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

I had to leave for a while , but I'm back with more info

I did extencive wire repair and removed all contacts and sanded lightly with sand paper. there was a clicking noise in the coil when i'd move the quick connect around with the key on. that dosent happen now after wire repair.

now,, with plugs removed from engine but on the plug wires, I get 1 spark at 1st revolution of the motor, then nothing,

today I'm pulling the flywheel to inspect the wires under it.

anything else I should do while i have it off?

Thanks guys!!

Doug

I do plan on marking the timing belt before removal,, hopefully the timing should be the same when i reinstall

 

[Wingedwheel]

Re: 1973 85 hp Merc,, Lost spark while idleing

It still sounds like you may have something grounding out. Did you check all your voltages?

 

[nomorefords]

Re: 1973 85 hp Merc,, Lost spark while idleing

Sorry Winged,,there are some important things I'm missing at the moment

1 manual
2 voltage meter
3 The education to use it
4 Money

I'm old school with basic knowlage of motors and how " most" of them work Through carefull inspection and prossess of elimination I'm trying to get to the bottom of this.

I had the control box apart and found 1 wire on the ignition that was losing insolation and repaired it.

I'm praying that today I find a bad wire under the flywheel,, if not,,I think I've reached my limit and have done all that I can do on my own.

You guys are heaven sent and dont realize what you mean to the average joe
I cant thank you enough

Thank you

Doug