63 Merc 3.9hp no spark

Teewayne

Recruit
Joined
Jul 15, 2013
Messages
3
I bought a 63 3.9hp at a garage sale. It looks clean, good compression, no spark. I hate to start replacing parts. Any ideas on where to start? Appreciate any input.
 

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: 63 Merc 3.9hp no spark

Pull the flywheel, clean the points to bare metal, polish with Crocus Cloth, degrease and gap the points to .020".

Use a harmonic balancer puller and (3) Grade 8 bolts of appropriate length/size to fit the puller holes in the flywheel.

Torque the flywheel nut to 35 ft-lbs and you should be ready to go!

Note: probably gonna need an impeller, too! Not to mention a little carb cleaning unless you were lucky enough to find one that was properly layed-up.

Here's one place you'll find parts diagrams, etc:

Mercury Marine 39 (1 CYL.) Outboard Motor Parts by Component

HTH...........ed
 

Teewayne

Recruit
Joined
Jul 15, 2013
Messages
3
Re: 63 Merc 3.9hp no spark

Sorry no pics yet.

I can get spark by grounding a bolt in place of the spark plug, but nothing with the plug. I've tried 2 new plugs but so far.....
 

bgc

Ensign
Joined
Jul 13, 2011
Messages
980
Re: 63 Merc 3.9hp no spark

emckelvy mentions some basics that should be done before trying to start the motor.
It takes less energy for the spark to jump at atmosphere then when under compression.
 
Last edited:

Teewayne

Recruit
Joined
Jul 15, 2013
Messages
3
Re: 63 Merc 3.9hp no spark

Changed the points and condenser and started right up! Not pissing properly so the impeller is next. Having a bit of trouble getting the cover to fit properly so the recoil starter functions. Thanks for the help so far!
 
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