bottom cylinder fouling plug

[dcmaker100]

i have a 1998 50 hp evinrude 2cycle 2 cyl vro.runs perfect all the time except once in a while,sometimes after 2 days of fishing,starting stopping,trolling,it will start easily then as im put it in gear and begin to give it gas it will go to one cylinder.i shut it off quickly and pull the bottom plug out which is wet.put in adry one and restart easily and it smokes a lot for a few seconds but fires perfectly and runs fine after that.the bottom plug seems to be getting too much oil,but only once in awhile.it will idle and troll for long periods without any problems.thanx for youre help

 

[OptsyEagle]

Re: bottom cylinder fouling plug

When the oil is coming from one carb and it sends it to both cylinders and only one cylinder is fouling a spark plug, I doubt it has anything to do with too much oil, unless perhaps the other plug was just about to foul.

In any event, for fouling plugs the first thing I would do is verify that you are using the right spark plugs. Your motor calls for Champion QL78YC spark plugs, gapped at 0.030".

The next thing I would want to do is ensure that my carburetor adjustment was correct (Rich/Lean adjust). Joe Reeves method here should direct you if you need it. http://forums.iboats.com/showthread.php?t=167352

The reason for plug fouling is improper burning of the fuel during combustion. This happens from the issues above, but also from running too cold from a malfunctioning or omited thermostat or bad timing as well as weakness in your the ignition spark.

 

[dcmaker100]

Re: bottom cylinder fouling plug

thank you i will start with the plugs when i can get back to it.how would i check the operation of the thermostat?the power pack is new and the coil was replaced once before,what other components would be suspected (weak spark)
that only affect one cylinder.

 

[Will Bark]

Re: bottom cylinder fouling plug

Agree with all of the above and you might want to consider decarbing the engine; I had one cylinder which was forever fouling out and after decarbing have no trouble since. You can look up how to do it in the top secret file at the top of this page. Good luck

 

[OptsyEagle]

Re: bottom cylinder fouling plug

thank you i will start with the plugs when i can get back to it.how would i check the operation of the thermostat?the power pack is new and the coil was replaced once before,what other components would be suspected (weak spark)
that only affect one cylinder.

I am not overly familiar with your engine but I would start with ensuring the correct spark plugs and ensuring the carb is adjusted properly. For spark, I would just do an external spark test with a spark tester and ensure your spark can jump a 3/8" gap. That will ensure that it is stong enough to burn everything and I wouldn't worry about timing. It is pretty much dictated by your powerpack.

As for checking your thermostat. The best way is to remove it. Usually you can see if it is corroded open since it should be closed when you take it out (it won't be corroded closed because that would be an engine overheat problem and you would already know about it). You can verify that it operates properly by putting it in pot of water on your stove. Stick in a thermometer and heat it up. You will see it just start to open around 145F and be completely open at 155F and when it cools it should close again. In any event, for plug fouling it would have to be stuck open or not be there at all. Some people take them out and if you never trolled much you might not ever have a problem. But OMC put them in there for the people who like to take their time on the water and a few more important reasons.

You should also go ahead and implement Will Barks decarb suggestion. Even if that was not what is causing your fouling, you can be sure that if carbon was building up on your spark plugs (that is what plug fouling is) then you can be sure it was also building up in your cylinders and piston rings, soon to become a more costly problem. Blow that crud out of there. I prefer to just take Seafoam (Deap Creap sprayable version) and fire it through the carb and then into the spark plug holes. Directions are on the can. The other method in the Top Secrect file has one putting it into the gas in large quantities. I prefer it not to go through my carb jets (what happens when it is in the gas) and discharge some crud in there that starts blocking up my carburetor. That is just my opinion. I do put a little seafoam (about 2%) in every tank to keep the crud from forming in the first place.

 

[dcmaker100]

Re: bottom cylinder fouling plug

I am not overly familiar with your engine but I would start with ensuring the correct spark plugs and ensuring the carb is adjusted properly. For spark, I would just do an external spark test with a spark tester and ensure your spark can jump a 3/8" gap. That will ensure that it is stong enough to burn everything and I wouldn't worry about timing. It is pretty much dictated by your powerpack.

As for checking your thermostat. The best way is to remove it. Usually you can see if it is corroded open since it should be closed when you take it out (it won't be corroded closed because that would be an engine overheat problem and you would already know about it). You can verify that it operates properly by putting it in pot of water on your stove. Stick in a thermometer and heat it up. You will see it just start to open around 145F and be completely open at 155F and when it cools it should close again. In any event, for plug fouling it would have to be stuck open or not be there at all. Some people take them out and if you never trolled much you might not ever have a problem. But OMC put them in there for the people who like to take their time on the water and a few more important reasons.

You should also go ahead and implement Will Barks decarb suggestion. Even if that was not what is causing your fouling, you can be sure that if carbon was building up on your spark plugs (that is what plug fouling is) then you can be sure it was also building up in your cylinders and piston rings, soon to become a more costly problem. Blow that crud out of there. I prefer to just take Seafoam (Deap Creap sprayable version) and fire it through the carb and then into the spark plug holes. Directions are on the can. The other method in the Top Secrect file has one putting it into the gas in large quantities. I prefer it not to go through my carb jets (what happens when it is in the gas) and discharge some crud in there that starts blocking up my carburetor. That is just my opinion. I do put a little seafoam (about 2%) in every tank to keep the crud from forming in the first place.

let me clarify what i mean by "fouling".The plug is wet.no carbon or any other deposit of any kind.the wetness looks mainly like mixed gas but sometimes looks like oil rich gas

 

[OptsyEagle]

Re: bottom cylinder fouling plug

Well your title and the fact that you took out a plug that was not working and put in a new plug and then it worked, gave me the impression that you fouled the bottom spark plug.

Oil and gas does not conduct electricity so having oil and gas on your spark plug should not prevent it from firing. Some of my other outboards, that work fine have a little wetness to the plugs after running. Probably a little worse if I am trolling a lot. Others are more tan and dry. The carbon comes from the combustion and can blend in well with the other tanish/oilish stuff that gets on the plugs. If it creates a link between the two electrodes of the spark plug, it will create a direct ground and of course no more spark.

In any event, have you verified what spark plugs you are using. I would say using the wrong plugs is the biggest curprit to plug fouling with the next the gas/air mixture for your carb.

 

[the machinist]

Re: bottom cylinder fouling plug

I agree with the previous answers, and I would also suggest you do a compression test.