1974 Evinrude 9.9 Plug Fouls

[Papaboat]

I run full speed, but after a few times trolling, I seem to loose full throttle when I am heading in. The boat won't come up on plane and every once in a while the motor will act like it gets more RPMS and then bog back down. I pulled plugs and one seems to be fouled up. Any ideas? I use 50:1 mixture.<br /><br />Also, the nut on the flywheel, is it a left handed thread? Thanks in advance

 

[JB]

Re: 1974 Evinrude 9.9 Plug Fouls

Howdy, Papa. What sort of boat do you have this 9.9 on? How fast and how long do you troll before the fouling shows up? Do I understand correctly that only one plug fouls and that it is always the same one? Do you get smoke when trolling?<br /><br />I don't recall whether that 9.9 used one or two carbs but it sounds like you have one cylinder idling (trolling) too rich or your plugs are too cold.<br /><br />Idling is an unnatural operation for most 2 strokes and frequently causes fouling and carbon buildup. Check your compression for balance and try decarbonizing it. Check your manual for a different plug recommended for extended low speed operation, and check the setting of your Carb mixture at idle.<br /><br />Hope that helps.<br />JB

 

[Papaboat]

Re: 1974 Evinrude 9.9 Plug Fouls

JB,<br /><br />Thanks for the reply.<br /><br />Seems that there is no pattern to how long I troll, it can be an hour and everything is ok, or it can be 10 minutes and then I have a problem. <br /><br />It is a single carb. And yes, seems to be the same plug that fouls. Any chance I could have a weak coil ?<br /><br />Also JB, I was going to look at the points, but having trouble pulling the flywheel off. Do you know if the nut has a left handed thread?<br /><br />Again, thank you for your time.<br /><br />Papaboat

 

[JB]

Re: 1974 Evinrude 9.9 Plug Fouls

Howdy, Papa. Could be a coil. Could be some intermittent electrical/ignition problem that you might find under the flywheel. I do believe that the flywheel nut is left handed (counterclockwise removes it). I would still want to know if the compression is balanced. <br /><br />Failing results on the above I would examine the reeds.<br /><br />Good luck.<br />JB

 

[Papaboat]

Re: 1974 Evinrude 9.9 Plug Fouls

JB, how do I check the compression? Thanks again..

 

[JB]

Re: 1974 Evinrude 9.9 Plug Fouls

First you need a compression guage. They are not very expensive, or you might have a buddy who can loan you one. There are two types: one with a rubber cone that you simply press into the spark plug hole, and one that screws into the sparkplug hole. If you have a choice, get the one that screws in. It is much more accurate and you can use it while operating your starter rope.<br /><br />Pull both spark plugs, attach the guage and spin her over. Note what the guage reads, typically 120 to 150lb. Now do the other cylinder. They should be within 10-15lb of each other and both over 100lb. If you have the kind of problem that could be causing your symptoms the cylinder that fouls the plug will be quite a bit lower than the "good" one.<br /><br />Let us know what you find.<br /><br />Good luck.<br />JB