surging engine

shearpin

Seaman Apprentice
Joined
Apr 23, 2006
Messages
37
Ok I've been working on a 1975 75hp evinrude. One cyl. #3 has shown signes of not running. it's been sitting for sometime. so I started out cleaning carb's, lines, fuel filter and change all three spark plugs. no change. I was using a timing light to check and see if the coil was working and acording to the light it was. Later I found out the that there wasn't enough juices to fire the plug. I replaced the coil and in the test tank it seemed to be firing on all 3 cyl. yet when I luanch the boat into the lake the engine seems to intermitingly fire on all 3 cyl. It realy feels like not enough fuel. recover the boat bring it back home and inspect the pluges. #3 plug where the boot of the pluge wire ends on the spark plug I can see carbon arking at the most 1/8 inch almost all the way around. Thinking the plug may be bad I replaced it. yet I still have the same problem and after running the engine the arking is back. running the engine with the cowling off (in a test tank) I hear the hi zapping. Could a slightly flooding cylinder (Vary rich due to float leavel) cause this to happen? I don't see the arking on any other plug.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: surging engine

The obvious is that you need to replace the plug boot. They are available without buying the whole coil.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: surging engine

Run the engine in the dark so you can see the arcing. Repair as needed.
 
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