Spark Plug Interpretation

Joined
Sep 18, 2002
Messages
5,539
Location
VA
Just took these out of my 1994 Honda Lawn Tractor. Been in for 2 years. What would make one plug run black? Now, I just cranked it up and let it run to get oil warm to change and then removed the plugs after it cooled down.
 
Joined
Apr 19, 2009
Messages
2,940
Location
Canada
That little bit of soot built up on the insulator is nothing. It's likely residue from running the machine with the choke on for start up. Had you run the machine under load for a while, chances are it would likely burn off. What's interesting though is that only one plug has soot on it as though only one cylinder was receiving more fuel? The sooty plug's electrode appears to be whitish. Which isn't unusual in today's lean running engines. You have nothing to worry about. The plugs look fine. The best time to read a spark plug is after running the engine under load for a good period of time. Normally the color should be a tan. But, as I said, today's very lean engines often show very light deposits. I have a 2005 Craftsman riding mower powered by a Honda GX engine. In the thirteen years that I've owned it, I've yet to pull the spark plugs. Engine starts quickly and runs strong. I've never felt the need to take a look at the plugs. Maybe this year.
 
Joined
Jun 15, 2003
Messages
37,973
Location
ME
When I had a v-twin bike one side was jetted differently from the other on account of cooling.
 
Joined
Apr 19, 2009
Messages
2,940
Location
Canada
That would make sense with one cylinder behind the other in a vertical installation. Especially in an air cooled engine. But in a horizontal, fan cooled V-twin, I doubt there would be a significant temperature differential between cylinders requiring different jetting and if the engine only has one carb, I'd say we can safely rule that out.
 
Joined
Jan 22, 2011
Messages
7,091
You have some oil control issue, compression or weak ignition associated with that one cylinder. That left plug is not acceptable and should look like the other. I have an old craftsman twin that did that, but not as bad, it was a bad magneto coil.
 
Joined
Apr 19, 2009
Messages
2,940
Location
Canada
Originally Posted By: Lubener
You have some oil control issue, compression or weak ignition associated with that one cylinder. That left plug is not acceptable and should look like the other. I have an old craftsman twin that did that, but not as bad, it was a bad magneto coil.
A little soot doesn't confirm that he has an oil consumption issue. He should just run the machine under load for a while then take a look at the plugs. If the engine isn't smoking blue under load, not likely to be an oil consumption problem.
 
Joined
Jan 22, 2011
Messages
7,091
Originally Posted By: boraticus
Originally Posted By: Lubener
You have some oil control issue, compression or weak ignition associated with that one cylinder. That left plug is not acceptable and should look like the other. I have an old craftsman twin that did that, but not as bad, it was a bad magneto coil.
A little soot doesn't confirm that he has an oil consumption issue. He should just run the machine under load for a while then take a look at the plugs. If the engine isn't smoking blue under load, not likely to be an oil consumption problem.
I suggest some oil because of the accumulated craters present. Minor oil consumption may not be bad enough to produce blue smoke.I use the common sense approach, if the plug condition is due to the way it was run,the other cylinder should look poorly as well.I would bet that compression results between the two cylinders are not similiar.
 
Last edited:
Joined
Apr 19, 2009
Messages
2,940
Location
Canada
Originally Posted By: Lubener
Originally Posted By: boraticus
Originally Posted By: Lubener
You have some oil control issue, compression or weak ignition associated with that one cylinder. That left plug is not acceptable and should look like the other. I have an old craftsman twin that did that, but not as bad, it was a bad magneto coil.
A little soot doesn't confirm that he has an oil consumption issue. He should just run the machine under load for a while then take a look at the plugs. If the engine isn't smoking blue under load, not likely to be an oil consumption problem.
I suggest some oil because of the accumulated craters present. Minor oil consumption may not be bad enough to produce blue smoke.I use the common sense approach, if the plug condition is due to the way it was run,the other cylinder should look poorly as well.I would bet that compression results between the two cylinders are not similiar.
Possibly could be some compression difference but once heated, would it be of any significance? Maybe the OP could tell us if the engine is consuming oil? If not, I wouldn't be too concerned about it.
 

Gebo

Thread starter
Joined
Sep 18, 2002
Messages
5,539
Location
VA
No oil consumption. Years ago I had a lot of misfiring problems. After talking with local dealer, changing plugs, etc., I ended up replacing both coils thinking it was low voltage. Come to find out I had a much simpler fix that I only figured out on accident. For years I had been washing and replacing the foam filter which covered the expensive paper element filter. The paper looked fine so I kept on using it and just washing and re-oiling the foam filter. Well, guess what? All my problems were fixed when I replaced the paper filter with a new one. It had gotten clogged with dirt that could not be seen with the naked eye. The clogged paper filter had been restricting air flow causing misfiring. Now I change both air filters every two years along with my gas filter and spark plugs. And only with Honda OEM. By the way, this is the GXV 620, V Twin, 20 HP Honda engine.
 
Joined
Apr 19, 2009
Messages
2,940
Location
Canada
Originally Posted By: Gebo
No oil consumption. Years ago I had a lot of misfiring problems. After talking with local dealer, changing plugs, etc., I ended up replacing both coils thinking it was low voltage. Come to find out I had a much simpler fix that I only figured out on accident. For years I had been washing and replacing the foam filter which covered the expensive paper element filter. The paper looked fine so I kept on using it and just washing and re-oiling the foam filter. Well, guess what? All my problems were fixed when I replaced the paper filter with a new one. It had gotten clogged with dirt that could not be seen with the naked eye. The clogged paper filter had been restricting air flow causing misfiring. Now I change both air filters every two years along with my gas filter and spark plugs. And only with Honda OEM. By the way, this is the GXV 620, V Twin, 20 HP Honda engine.
I could be wrong but I don't think you're supposed to oil the foam filter if it's over a paper filter. Doing so would cause the paper filter to become saturated and too restricted if oil gets on it in sufficient quantity. I've been using the original paper filter on my Honda GXV-530 for going on 13 years. I use compressed air to blow both the foam and paper elements out every so often. It's not very dusty where I cut so, the filter doesn't pull in much dust. Does your GXV-620 have overead cams? My 530 does, which I thought was unusual. Most GX engines are push rod.
 

Gebo

Thread starter
Joined
Sep 18, 2002
Messages
5,539
Location
VA
boraticus, You make an excellent point about oiling the foam filter. I know when it is still in the plastic bag there is a little oil in there with the filter. Maybe I was over oiling it. I'll start a new thread on the "oiling the foam."
 
Joined
Jan 22, 2011
Messages
7,091
Originally Posted By: Gebo
boraticus, You make an excellent point about oiling the foam filter. I know when it is still in the plastic bag there is a little oil in there with the filter. Maybe I was over oiling it. I'll start a new thread on the "oiling the foam."
If that were the case, the other plug would be blackened too. Look elsewhere.
 
Top