1972 merc 120 died and wont start

[cchildress142]

Need some help!!! I have a 1972 merc 120 in a 17' Larson. Got the boat a month ago from a friend and started the restoration. Been running great til last week the coupler gave out. Pulled the motor last night, installed new coupler and put engine back in. Started it this morning and ran fine for about 10 minutes idling. Tried shifting into gear a couple of times and before i could see about how the outdrive was doing the motor died. Just like i had cut the switch off!! Now it wont start at all. Checked fuel, good. Checked all wiring, etc that was removed for the engine pull, all good. It has new coil, points, condensor, rotor cap, plugs and wires. Where should i start first??? Thx for the help guys. Im a newbie to the boat world and not a world class mechanic!!

 

[stonyloam]

Pull the center wire from the distributor, place it near bare engine metal, crank it over to see if you have spark.

 

[stonyloam]

BTW did you realign the engine ( with a a alignment bar)when you reinstalled it? If not then the coupler is likely to fail again. Just asking because you did not mention it.

 

[Fisnfool]

Does it crank or you have nothing at all? If not cranking, check the neutral safety switch, often located in the shift control. It should have continuity in neutral only. If not, then the switch failed. Do you have a service manual? If it cranks and no spark as tested in comment 2, check the shift interrupt switch located at the stern on the shift mechanism. This switch is designed to split second cut off the ignition as you shift to make shifting easier.

 

[Fisnfool]

I forgot to mention, See the Adults Only sticky. The title is just to get people to look. See #5 for engine alignment, and #9 for the shift interrupt. #15 is ignition trouble shooting. Click on the blue f. It will open the link for you.

 

[Fisnfool]

If you do not have a service manual, you can look at one using this link. Click on the stack of books next to the anchor. Chose the brand, then click on service manual #1. It covers your model year.

 

[Bondo]

Need some help!!! I have a 1972 merc 120 in a 17' Larson. Got the boat a month ago from a friend and started the restoration. Been running great til last week the coupler gave out. Pulled the motor last night, installed new coupler and put engine back in. Started it this morning and ran fine for about 10 minutes idling. Tried shifting into gear a couple of times and before i could see about how the outdrive was doing the motor died. Just like i had cut the switch off!! Now it wont start at all. Checked fuel, good. Checked all wiring, etc that was removed for the engine pull, all good. It has new coil, points, condensor, rotor cap, plugs and wires. Where should i start first??? Thx for the help guys. Im a newbie to the boat world and not a world class mechanic!!

Ayuh,.... Welcome Aboard,...... Does it crank over on the starter, 'n not Start, or What,..??

If so, is there Power at the coil's (+) terminal, with the key "On",..??

If Not, Clean the Battery terminals, 1st,.... Both ends, of Both wires,....

 

[mr 88]

The first thing I would do is remove the interupter switch wire from the negative side of the coil.pretty sure its the gray one,then try it. And or make sure you reinstalled the ground wire from the interupter switch to the back of the block.