'71 Merc 800 no spark?

Phil303

Seaman
Joined
Jul 25, 2009
Messages
55
Hi All,

I have a 71 merc 800 serial 3052172.

It stood for a number of years,i got it going, it ran good eventually....

I ran it with a maintenance free car battery to try it out.

i ran it for 4 or 5 mins fine, then i switched it off by choking it. the kill switch was duff.

Since i stopped it i no longer get spark at all? i get nothing as far back as the coil..

I've read a lot hear on iboats, very useful!

i read through the ignition checks to do.
I get 12.8V at the red on the switchbox all the time.
I get 12.8V on the White when i switch to run.
when i crank it it drops to 9V

and as i said i get nothing on the lead from the coil.

Is there some way i can test the green wire to see if the power to the coil is good? i don't know anyone with peak voltage reader? can i do it with my multimeter?

The coil has quite a few cracks in what look like the magnets around it? they were there before though when it was running fine so i'm not really suspecting that as the fault?

i tested the resistance of the coil and it seems ok but a little wierd?

could running maintenance free batt or just the batt being a bit crappy charged cause this sudden loss of spark?

could i have toasted the switchbox running it for 4-5 mins? i would have thought if switchbox was toast it would have stopped on its own, and not by me stopping it?

thanks for your help.

Phil
 

SeaKaye12

Lieutenant Junior Grade
Joined
Jul 3, 2005
Messages
1,107
Re: '71 Merc 800 no spark?

You can have one of the pros here walk you through a test of the ignition system...but first off I'd look over all the wiring really carefully.

On mine I lost spark while idling at the dock. Sure enough; one of the wires leading to the trigger essentially disintegrated; way up under the flywheel where I couldn't see it.

Old Mercury wiring is notorious for having problems.

Good luck
 

Phil303

Seaman
Joined
Jul 25, 2009
Messages
55
Re: '71 Merc 800 no spark?

am i right in thinking this engine should run even if the stator wasn't connected?

it would then only run on battery power, ok it wouldn't charge but it should still run right?

i think the 2 wires from the stator are a bit corroded, does that mean i have to pull the flywheel and follow them back, is it possible to replace them or is it all built as one? i hear stators are pretty pricey $$$
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,033
Re: '71 Merc 800 no spark?

Yes, the distributor ign motors do not depend on the stator for spark. There is a dist ign test on this forum as well as the CDIelectronics.com website. It presumes your coil is good. If yours has cracks, you should replace it, and then test the ign.

See if you can solder a new wire onto the stator. You can remove the stator for surgery, by removing the 8 5/16" bolts that ring the flywheel nut. Set the motor to TDC so you may reinstll the outer flywheel properly. use some blue locktight on the 8 bolts.
 

Phil303

Seaman
Joined
Jul 25, 2009
Messages
55
Re: '71 Merc 800 no spark?

chris,

thanks, i'll try do that with the stator wires,

i went back over some coil tests my book suggested, my multimeter doesn't do multiples of x1, x100, x1000 and so on.... only x200, x2000, x20,000 etc.... so i'm not sure if i need to adjust the readings at all?

on 200 ohms on positive to negative i get 0.4

on 2000 ohms from coil tower to either neg or pos i get 660?

on 200 ohms from coil tower to grnd there's no read, i tried it on 20,000 and it read 10.5?

What do you think of these numbers? is it a bin job?


I've looked all over for replacement and i can't find one anywhere? is it possible to use a different model coil from another engine perhaps? don't they all do the same thing, turn volts into mega volts for sparking?

cheers for your help.

phil
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,033
Re: '71 Merc 800 no spark?

There is a standard coil for the later inlines with Dist ign. That one should work for you. They are aftermarket. Look for a coil for a '77 Inline six, as an example. You may need to find a new way to mount it, and the later coil has three 5/16" stainless bolts to mount it on the crankcase cover. Yours is likey mounted in them bottom cowl.

I am not sure it is useful to ohm out your coil. it may test perfectly, but arc to ground because of the cracks.
 

Phil303

Seaman
Joined
Jul 25, 2009
Messages
55
Re: '71 Merc 800 no spark?

I just looked for a '77 inline 6 coil and i found a part number for one, it's the same as mine. 332-4895

That's the part i can't seem to get hold of? i was hoping there was an alternate part number that did the same job?
 

Phil303

Seaman
Joined
Jul 25, 2009
Messages
55
Re: '71 Merc 800 no spark?

i went for part 337-4456...

when i install it, is there anything i need to watch out for, so i don't toast something else?

i still have the battery question? is it ok to use a maintenance free battery?

thanks

phil
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,033
Re: '71 Merc 800 no spark?

Yeah that second used one and the new Sierra coils look like the ones on my '77 IL6. I would buy the new Sierra one, if it were me.

Maintenance free batteries are not recommended since the charging system is unregulated, and if you run the motor a lot at high speed, you will eventually boil all the water out of the battery. With the 6A charging system you have, that would take a whole lot of hours, likely more than you will ever get out of the battery. A lot of those batteries have filler caps for the cells, hidden under the top decal. If yours can be refilled, you will eliminate any remote danger of boiling them dry.
 
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