One spark plug dry

[onebohemian]

I've got an '87 Evinrude V4 90 horse. Just got it on a boat I bought. I ran the motor a couple of minutes with a motor flusher attached. About an hour later, when the motor was cool, I pulled the spark plugs to see how they looked and make sure they were set properly. One of the four spark plugs was completely dry, no oil/gas on it at all. The other three were all damp at a minimum. I've run the boat on the water a couple of times and she ran great. I didn't hear or sense any missing in the motor. Seemed to pull fine with plenty of smooth power throughout the throttle.<br /><br />My question is what problems might this indicate? Also, what tests can I perform to check any of these problems out? I'm thinking that I should run the motor and pull the plugs again, that maybe just idling in my driveway had something to do with it (but I'm also thinking that this may be wishful thinking on my part).<br /><br />Thanks in advance, <br /><br />Mark<br />Minnesota

 

[Joe Reeves]

Re: One spark plug dry

Onebo..... Just exactly what did that one dry spark plug look like....<br /><br />Dry, black, and fluffy? Dry, brown colored? Dry, and white? Dry, describe color, small hard beads on the porcelain?<br /><br />What did all of the other plugs look like?

 

[onebohemian]

Re: One spark plug dry

The three plugs that were wet/damp had gas/oil mixture on them, enough that I could wipe a little off with my finger but not anywhere near dripping. The dry plug was clean and had a nice grayish/sandy color to it. It's not burnt. It just looked like a decent plug. The dry plug looked like there wasn't any mixture getting to it recently. At the time, my first thought was that this might have been the only plug that was actually working properly (or that the carb attached to this cylinder is probably the only one introducing the correct mix of gas/oil and air and that the others are actually being flooded somewhat. But I'm now leaning toward the problem being with this one dry plug and/or its cylinder and carb.<br /><br />I have to believe, however, that I would have been able to tell if only three of four cylinders were working when I had the boat on the lake, or even when it was just idling in my driveway. I'm not a professional mechanic, but I grew up on a farm where we did most all of our own fixing of equipment, I do all of my own service on our vehicles, including tune ups, I adjust valves and clean carbs on motorcycles, etc., so I have a pretty good sense of what motors are supposed to sound like when their running well and when there's a whole cylinder out. I've just never seen one plug out of all the rest be dry before. I've seen it the other way around on some other motor where one plug is fouled, but then it's dripping gas or has some carbon built up on it.<br /><br />Any thoughts would be appreciated.<br /><br />Mark<br />Minnesota

 

[Steve135]

Re: One spark plug dry

Hey did you ever find out an answer? I have the same thing on a 150 6 cyl with one plug light brown dry the rest wet.<br />steve

 

[dajohnson53]

Re: One spark plug dry

Just in case this helps - I recently went for a ride on a friend's 4 cylinder (happended to be a yammie, but ...). Anyway, his engine was functioning on only three cylinders. Symptoms were first and foremost, loss of power on acceleration and WOT RPMs approximately 25% less than normal (4000-some instead of 5000-some). It was the first time I'd ridden in it and it didn't sound "bad" to me - but the guy, who had run it many times of course, knew it was sluggish and not winding out.<br /><br />In his case it wasn't a "dry" plug, but one that was obviously fouled. We changed it and the motor ran great and got it's normal WOT RPMs. He hadn't changed the plugs in a season or two. I would assume that if the "dry" plug was not getting fuel, you'd have to have some similar symptoms - sluggish and loss of WOT RPMs?? <br /><br />Not an expert, just relaying a recent experience.

 

[woody74]

Re: One spark plug dry

You are running a two stroke where the plugs eventually are supposed to look "wet" but dripping. This means that the cylinder is getting lubed. So the one clean plug sounds like an ignition prob and not a fuel one. I had this happen on a motor of mine and as soon as I rebuilt the ignition I had restored power and two "wet" plugs. -woody74

 

[woody74]

Re: One spark plug dry

Ooops I meant NOT dripping... -woody74

 

[woody74]

Re: One spark plug dry

Oh yeah, its hard to even tell on two cylinders at idle if you have a cylinder out. I am assuming you had it at idle or somewhere about when flushing. Its just so much easier to tell at WOT than at idle thats all...JMTC -woody74