View Full Version : oily plugs 1975 evinrude 9.9

10-25-2005, 12:05 PM
for the past 3 months i have been having motor problems that i never had b4. pic is example of my problem, those were clean new plugs but turns moisty black after 4 hrs of trolling. when i go to throttle and jam back to the ramp horsepower is way down becuz of this i think. only if i stop fishing and trottle up everyonce in awhile this wont happen it clears out the deposits on the plugs. or if i take them out and clean them, its all good. im using 50/1 and 89 fuel, compression is 95 on both. lower plug doesnt get as bad. why is this happeneing.


10-25-2005, 01:43 PM
You are running too rich. This has nothing to do with the amount of oil you are using in your fuel. If you are operating at high altitude, you may need to have your carb re-jetted. Otherwise make sure that you are using NGK's and move up a heat range to a hotter plug.

10-25-2005, 05:49 PM
i turn the dail a lil to the lean when i go up. i also tend to speed troll too.

10-26-2005, 08:55 AM
What did you change about four months ago? *Are you now at higher elevations? *
a lil probably isn't enough. *Like Doc said your carbs might need to be re-jetted and you might need to go to a hotter plug.

10-26-2005, 05:50 PM
nothing has changed as far as how and where i fish. but ill try hotter plugs and try to go even leaner. 8) ty

10-26-2005, 06:44 PM
1 carb for 2 cylinders or 1 carb per cylinder? 1 coil pack or 2? it could be more than just a carb problem.it could be spark related under a load.like,,a bad wire or coil could also cause 1 plug to fowl out at low rpm under a load.if it's only 1,the same plug all the time it could be the carb for that cylinder.or that coil or wire.or a problem with rings or piston or head but if you did a compression check you ruled that out.switch wires from 1 side to the other and see if the same plug fowls.

10-26-2005, 07:52 PM
Going leaner with the mix probably isn't the answer. You could end up compromising your lubrication and stick a ring. I raced desert for many years, and there was only one oil that we ran at 100:1. I don't believe it's around any more. Before attempting to re-jet, put in some new plugs and run it WFO across the lake and immediately shut it down. Pull the plugs and they should be a nice milk chocolate color. If they are black and wet, you are too rich. You may then want to pull the carb(s) and look for some smaller jets. If you do take apart the carbs, be sure to buy 3 or so steps down, in case one step isn't enough.

Also a good idea as stated above:
"switch wires from 1 side to the other and see if the same plug fowls"


10-27-2005, 10:02 AM
why would i switch the 2 plug wires? i have new coils in it. the one plug that doesnt get as bad still gets bad.

10-28-2005, 07:55 AM
To isolate the problem, process of elimination, new part does not = good part, knowen good part i.e part from another source to be used as test part to secure source of problem...good luck! :)

11-02-2005, 07:52 AM
the easiest way to burn a piston in a 2 stroke is to run lean and use a hotter plug. A hotter plug wont get rid of the problem, your carb is wacked, the floats are saturated or a needle valve is stuck part open. Thats an old motor ao I bet the carbs are about as old also. Why I say this is that it ran good for how long? Then started fouling the plugs? If you have a bad coil, plug or wire you are going to get a bad miss and a rough running motor.

11-03-2005, 10:22 AM
Changing the plugs to one higher heat range will have no significant effect on the operating temperature of an engine. Only the temperature of the spark plug tip. The plug will just will not last as long during operation at higher speed and temperature. Engines used primarily for trolling require a higher heat range plug than those operated at speed.

Running too lean will cause an engine to overheat and could burn up a piston. If you re-jet for high altitude, you MUST go back to the stock jets for sea level operation.

Here is some useful info on the topic:


11-04-2005, 09:24 PM
tried the switch the wires thing. wont even star when i do that. *if lean is 0 and rich is 100% on the dial, i put it on 25%, and no more problem so far. b4 i was running it at 45% at high elevations. and 50% at low ele.

11-05-2005, 05:47 AM
There is a simple way to get the mixture right on those older 2-strokes: With the engine in neutral and warmed up a bit, goose the throttle as you decrease the mixture setting. Whatever setting just gets rid of the lag in response at a given altitude is approximately where you want to be.

11-05-2005, 08:58 PM
died out on me today at stumpy. wouldnt start after it died, then i pulled the plus to clean them(pretty bad). started up a few times and died then nothing after that. found out today at cals, i am using the hottest of plugs i could be using 4 it. which are the recommended plugs. was told to try mercury power tune enigine cleaner to clear out all the carbon depsoits. spray it in the carborator while running until it dies then wait 20mins or so and to do it a few times. so im gunan try that this week at home.

11-11-2005, 01:46 PM
used that powertune spary a few times, replaced the impeller as well. gunan see what happens this weekend. hopfully i got the lower units in gear right. the lower unit some how went into nuetral when it was off. ??? but its seems to be back, a few times in forward gear it isnt(prop spins both ways) until i put it in reverse and to 4ward again. im gunna test it tomarrow