Mercruiser 120 no spark help!!!!!

floridaboater1

Petty Officer 3rd Class
Joined
May 20, 2010
Messages
80
I have a 1975 mercruiser 120 fully rebuilt. I went out to start it yesterday and i have no spark. It hase a new coil. condenser. points. cap. rotor. wireing. I have power and ground to the coil. the distributer is spinning. Is there anything im overlooking?
 

45Auto

Commander
Joined
May 31, 2002
Messages
2,842
Re: Mercruiser 120 no spark help!!!!!

Check that the baseplate of the points is grounding to the baseplate of the distributor. Clean them both up with a little sandpaper. My '82 120 used to lose spark regularly when the baseplate got just the slightest bit corroded under the points.
 

fishrdan

Admiral
Joined
Jan 25, 2008
Messages
6,989
Re: Mercruiser 120 no spark help!!!!!

Points gapped properly?
Get spark from the coil if you manually open the points?

Besides the normal ignition troubleshooting, check to make sure the shift interrupt switch is not grounding out the ignition. It's supposed to momentarily ground out the ignition while shifting out of gear, but could also shut down the ignition if the switch is bad, switch adjusted wrong, switch held closed, wire is grounded out. Disconnect the (brown?) shift interrupt wire from the coil and see if it starts. If it does, troubleshoot from there.
 

dpoff

Petty Officer 2nd Class
Joined
Nov 27, 2004
Messages
169
Re: Mercruiser 120 no spark help!!!!!

Rotor installed? Been there!
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Re: Mercruiser 120 no spark help!!!!!

I believe you should have 9v to the coil.Or have a coil with a resistor to drop the voltage to 9.
Measure the voltage through the coil. The points that are available are cheap and short out easily.Carry a set of points and condenser as a backup.J
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: Mercruiser 120 no spark help!!!!!

Besides the normal ignition troubleshooting, check to make sure the shift interrupt switch is not grounding out the ignition.

That's a real good point - something easily overlooked and just as easy to check.
 
Top