weak spark on 1969 Mercury 350

Joined
Jun 28, 2003
Messages
16
I have a 1969 Mercury 350 (S/N 2572263) that refuses to start. First off, I was unable to get a spark from either cylinder. I replaced both magneto coils, condensers, points, spark plugs and spark plug wires. I set the points @ .020 and max spark on #1 cylinder @ .300 btdc. I still only get a weak votlage reading from the spark plug wire(usually 5000vdc) just a small tingle when I hold the wire. I cleaned the stator really good with same results. I've replace everything! Any ideas on where to go from here!!
 

ratt1966

Seaman
Joined
Jun 21, 2003
Messages
58
Re: weak spark on 1969 Mercury 350

you could always sell it to me just kidding check that you wiring harness is in good condition and that you have good conection where 12 volts goes to coils
 
Joined
Jun 28, 2003
Messages
16
Re: weak spark on 1969 Mercury 350

thanks ratt1966 I removed the wiring harness when old coil started smoking. didn't think 12 volts is suppose to reach the coil. Does this help step up the voltage to the spark plugs?
 

ratt1966

Seaman
Joined
Jun 21, 2003
Messages
58
Re: weak spark on 1969 Mercury 350

yes it is supposed to have 12 volts to the coil it comes from the switch i have a wiring digram if you need it just give me your email and i will send it to you you will need acrobat reader to view it
 

ratt1966

Seaman
Joined
Jun 21, 2003
Messages
58
Re: weak spark on 1969 Mercury 350

just sent that file to you let me know if you got it hope it helps
 
Joined
Jun 28, 2003
Messages
16
Re: weak spark on 1969 Mercury 350

yea i got the file. thanks had to check measurements before installing on boat and insure wiring correct. here is what I got<br />switch off<br />white- grounded/ point e-d<br />salmon- grounded/ point f-d<br />switch on<br />white-3.8vdc/ continuity between e-d<br />salmon-12.3vdc/ continuity between f-d<br />I'm not sure if these are correct but will install to motor tomorrow. just hate to fry my new coils. I'll keep you posted
 

ratt1966

Seaman
Joined
Jun 21, 2003
Messages
58
Re: weak spark on 1969 Mercury 350

that sounds about can't check mine my harness is tost so i took it off am looking for another one good luck repost a new message if you have any more questions.
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: weak spark on 1969 Mercury 350

That motor is NOT supposed to have 12V going to the ignition coils. It has a self-contained magneto ignition - no battery required. Make sure the points are clean - run a strip of index card dipped in lacquer thinner or carb cleaner through the points to get any oils, grit, etc. out of the points.<br /> Make sure the ignition kill wires are in good shape and not grounding out. These are the two wires that lead from a block terminal on the motor block to the points. The terminal will also have two wires leading to the harness plug. I had one once with no spark - turned out to be the previous tinkerer had used screws that were too long in the terminal block and they grounded through the other side in the motor block.<br /> Drop the point gap down to .018". <br /> Also, where did you get the condensers? If they are new old stock (.ie on the shelf for 30 years), they may be bad. I've had good luck with Sierra ignition parts, available through NAPA.<br /> I've got two of these 35hp twins ('66 electric & '69 manual tiller) - great runners...<br />- Scott
 
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