Mercury 7.5 HP no spark

[Robertw]

I am trying to get a 1971 7.5 hp Mercury Comet outboard motor running but have no spark. I have checked the wiring and found no breaks etc. The points are used but dont look too bad.I did find the kill switch was corroded and was not connecting to ground. Could anyone tell me how to test the stator (p/n 336-3996)?

 

[12Footer]

Re: Mercury 7.5 HP no spark

The kill switch connects to ground to kill the ignition.<br />Try disconnecting the kill switch to see if it is shorting the stator to ground (how it kills the engine().<br />Check for corrosion at the stator connections by removng them one at a time.<br />If original, there will be two of these connectors from the stator.

 

[Robertw]

Re: Mercury 7.5 HP no spark

I have tried disconnecting the kill switch wire with no effect. I get no voltage on the green wire (to the ignition coils) with the orange wire connected to the kill switch or disconnected. I do get about 45v peak on the orange wire when it is disconected from the kill switch. Do you know what the impedance on the wires should be?<br />Thanks

 

[Rex]

Re: Mercury 7.5 HP no spark

FIRST CHECK TO IF YOU GOT VOLTAGE TO THE POINTS. IF SO CHANGE THEM JUST BECUSE THEY LOOK GOOD DOES NOT MEAN THEY ARE.<br />THE EASY WAY TO DO IT.<br />IS JUST PUT ALL NEW IN.<br />BUT I WOULD START WITH THE POINTS.CHEAP.

 

[corm]

Re: Mercury 7.5 HP no spark

check the white insulators that the points connect to to see if they are cracked and shorting to ground. on the wire side not the stud side. I'd need a serial no. to get you the correct specs.<br /><br />corm

 

[Robertw]

Re: Mercury 7.5 HP no spark

Yesterday I had a friend look at it, he figures it could be the points. They look like the original ones. And on closer inspection the white insulators are cracked. As this motor belongs to a friend I will have him order a new set of points. The serial number is 4368-51578. We really want to get it running as his 70hp Evinrude runs too fast for trolling.

 

[corm]

Re: Mercury 7.5 HP no spark

The points are less imporant than the insulators. If the pts are pitted so bad that<br />they can't be set at .020 then maybe you could replace them. Use L77J4C plugs gapped at .040 the motor will idle much better for you. I don't have any books at home to look up the stator specs, but will try to remember to look for you.

 

[Robertw]

Re: Mercury 7.5 HP no spark

Thanks for the info. We worked on it the other night and cleaned up the points. Now we get intermittent spark. The owner of the motor is in no rush to order any parts for this motor as fishing season is almost over.