1975 evinrude 25hp problems

[tombold]

I have a 1975 25hp evinrude outboard, I have been having some misfire problems. I went to change out the plugs and discovered that the spark plug threads were stripped, so I pulled the head and am in the process of getting the helicoil installed. Also, when I was pulling the head I noticed the bottom 2 head bolts were looser than the others causing fuel leakage. When I got the head off I noticed the top cylinder was very clean with little carbon build up, but the lower cylinder was considerably more gunked up that the top. Also, the plugs that were in it were Champion L77LC4, which my manual calls for JC4. Would the loose lower head bolts, plugs, and the stripped plug threads cause a misfire? Any help would be wonderful.

 

[wilde1j]

Re: 1975 evinrude 25hp problems

While you have the head off, carefully inspect the head and the block for any signs of water intrusion, which is likely the reason for the upper piston and head being so clean. Were both plugs holes stripped? That can lead to a burned piston and other anomolies. Make sure the block and the head are perfectly flat, use a new head gasket and torque the head bolts. Retorque the head bolts after about 10 hours of running time.

 

[tombold]

Re: 1975 evinrude 25hp problems

Thanks for the reply, I will clarify. I mean clean as in no excessive carbon on the upper cyl. (good burning) Everything looked good, no signs of water intrusion, I have a new head gasket on the way and the lower cyl was the only stripped cyl. The lower cylinder had considerably more carbon buildup. I am assuming that at some point the prevoius owner had overhauled the motor, I am only using an educated guess. Would the incorrect spark plug (see prevoius post) have anything to do with it. Thanks

 

[wilde1j]

Re: 1975 evinrude 25hp problems

Incorrect plugs are not good. I don't have info on your motor, but a dealer or someone else here should have correct Champion number for your motor.

 

[Joe Reeves]

Re: 1975 evinrude 25hp problems

The 1975 25hp has standard ignition and will not operate properly with the QL77JC4 or L77JC4 spark plugs regardless of the gap setting.<br /><br />The engine originally called for Champion J4J spark plugs which are no longer used. They were upgraded to Champion J4C plugs, with an alternative plug being J6C. The "C" indicates a copper electrode for longer life. The J6C plug is slightly hotter and usually improves performance on the older engines.... a matter of choice and preference.

 

[tombold]

Re: 1975 evinrude 25hp problems

Thanks for all the great information, I got some new J4C plugs. I will make sure to use all the great info you provided.

 

[Crazy]

Re: 1975 evinrude 25hp problems

Ya your head bolts being lose ... didn't help you out any ... good thing you cought it in time , the side with the lose bolts was sucking air and running Lean , that's why it was clean . fix you plug hole and change the plugs should fix your problem . Good luck