spark plug picture after 10 hours...running lean?

[94OMC]

Hi everybody.

My 5.0L OMC SX on a 19' Four Winns open bow is only hitting about 4k rpm at WOT. It should be closer to 4400 rpm. So I pulled the plugs to check compression (all are between 135 and 145 psi). The plugs were new at the beginning of the year, and I'm guessing the engine has about 10 hrs on it since spring. Here's a pic of the #2 plug (all 8 of them looked just like this).

I'm a little concerned by what appears to be some erosion of the insulator. The insulator is also a little more white than I'm used to, but these plugs don't have a whole lot of use on them...

Would a lean condition cause the plugs to look like this? The gap was set correctly @ 0.035" If it is running lean, that would probably explain why it's only hitting 4k WOT. The boat has plenty of power out of the hole, but runs out of steam after 3500 rpm.

thanks in advance..

 

[PINESOL]

Re: spark plug picture after 10 hours...running lean?

honestly i dont see much wrong with that plug ..may just be the pic. by your description you may be running lean though .. is it a 94 ? carb or inj. richin it up a little if its carb and see if that corrects your wot range ...

 

[94OMC]

Re: spark plug picture after 10 hours...running lean?

Pinesol - yes the boat is a '94 and it has a 2-bbl carb.

 

[Deanrw3]

Re: spark plug picture after 10 hours...running lean?

Looks fine to me IMO. It seems to have a light to dark brown color, which is good.

If it was lean/hot it would be white, if i recall.


Change the settings if needed and run them a little more and check again.



GL

Dean

 

[bjcsc]

Re: spark plug picture after 10 hours...running lean?

Did you shut the engine down at a high RPM or did you pull it down to idle and then shut it down? If the latter, how long did it idle before you shut it down?

 

[94OMC]

Re: spark plug picture after 10 hours...running lean?

Did you shut the engine down at a high RPM or did you pull it down to idle and then shut it down? If the latter, how long did it idle before you shut it down?

I never shut it down from a high RPM. It always has at least 30 secs of idling before I shut it off...

 

[Bondo]

Re: spark plug picture after 10 hours...running lean?

Ayuh,....

I donno,... Maybe it's just Me,...
But I see either an Awfully Clean, or Detonated plug.....
It could be Clean from Water injestion,....
Or maybe Way Lean, or Over Advanced timing....

On the Ground Strap,... Top corner, nearest the electrode, is that a Speck of aluminum,..??..??
How about right on the Corner, upper outside of the ground strap's Bend,....
Speck of aluminum there too,..??..??
Kinda looks like Boiled Piston.....??

 

[WizeOne]

Re: spark plug picture after 10 hours...running lean?

Looks pretty lean to me, especially after idling. The silver on the threads and seating surface??? could that be an anti-sieze compound?

If they all look like that, and your carb is not new, I'd be looking for a vacuum leak.

 

[JustJason]

Re: spark plug picture after 10 hours...running lean?

tough to say just by looking at that picture. I'd be more curious to know what the insulator looks like down deep, not just the tip.
It's a bit tougher to read plugs these days because ethanol cleans them....
The other thing to remember with V8 carbed motors is that the 4 corner cylinders tend to run a bit leaner, and the 4 core cylinders tend to run a bit richer.... it's carberation we're dealing with so they don't obviously meter fuel as well or efficiantly as injectors.

this is a good read for anybody... so read this.

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

 

[94OMC]

Re: spark plug picture after 10 hours...running lean?

I've never seen or heard any symptoms of detonation, and I run the correct octane (89) with a bit of sea foam, so hopefully it's not detonating...

The engine has never over heated since I've had it. Who knows what happened in it's prior lifetime, but these were new plugs this spring.

I'll check for a vacuum leak, as I haven't tried that yet.

Last fall, I poured some sea foam through the carb, and this spring I sprayed a bunch of carb cleaner through it. Other than that, and adjusting the idle, I haven't touched the carb.

I checked the timing a month ago and it was right on spec.

Other than only hitting 4000 WOT, the engine runs really great. Starts right up, idles smooth, no hiccups during acceleration. It just seems to run out of steam after 3500 or so.

Right now, I'm leaning towards a lean condition. Excuse the noob question here, but do I richen it up a bit by turning the idle mixture screws out?? It's a Holley 2-bbl.

thanks

 

[Mkos1980]

Re: spark plug picture after 10 hours...running lean?

My plugs look identical too. All 8 of them. Looks like I just pulled them out of the box. Motor has about 10 hours also. 350Mag 4bbl here.

 

[bjcsc]

Re: spark plug picture after 10 hours...running lean?

Right now, I'm leaning towards a lean condition. Excuse the noob question here, but do I richen it up a bit by turning the idle mixture screws out?? It's a Holley 2-bbl.

The idle mixture screws will only affect the mixture at.......idle! You would have to change the jets to affect the mixture at high RPMs...

 

[marada1]

Re: spark plug picture after 10 hours...running lean?

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

 

[MikDee]

Re: spark plug picture after 10 hours...running lean?

Ayuh,....

I donno,... Maybe it's just Me,...
But I see either an Awfully Clean, or Detonated plug.....
It could be Clean from Water injestion,....
Or maybe Way Lean, or Over Advanced timing....

On the Ground Strap,... Top corner, nearest the electrode, is that a Speck of aluminum,..??..??
How about right on the Corner, upper outside of the ground strap's Bend,....
Speck of aluminum there too,..??..??
Kinda looks like Boiled Piston.....??

I'm with Bond-o on this one, those plugs look washed to me?, water injestion

 

[flabum]

Re: spark plug picture after 10 hours...running lean?

How's the compression?

 

[bjcsc]

Re: spark plug picture after 10 hours...running lean?

I never shut it down from a high RPM. It always has at least 30 secs of idling before I shut it off...

While that is good practice in general, it obscures plug reading. If you want to know what's going on at 3500RPM, you have to hold it there and then cut it clean, i.e. turn it off without idling first. This is tough with a boat as that same practice can cause water ingestion...

 

[bayliner in elkmore]

Re: spark plug picture after 10 hours...running lean?

the plugs look very clean! water?? but hows your prop look?

 

[94OMC]

Re: spark plug picture after 10 hours...running lean?

What are some symptoms of water injestion? I don't have any adverse symptoms other than a lack of power/WOT RPM. The boat always starts right up and idles just fine.

FYI - I put a new set of plugs in the boat after checking the compression a couple weeks ago (wasn't planning on it, but I broke a plug). The new plugs still look very clean after 3-4 hours. I even pulled the plugs directly after letting the engine idle on muffs for a half hour, and they all looked just like the pic in the first post. Would Seafoam in the gas keep the plugs looking so clean?

Oh, and the prop looks brand new. Had it repaired before boating season began this year. Based on the markings, I believe it is the same prop (SS) that came with the boat in 1994.

 

[Maclin]

Re: spark plug picture after 10 hours...running lean?

I am used to seeing a light brown pattern developing on the white insulator, so I would think that those show lean like you suspect.

And idling down for a while after a high speed run typically would fatten things up so the plugs should tend to have a sootier look if that is what happened just before you took them out.

 

[MikDee]

Re: spark plug picture after 10 hours...running lean?

What are some symptoms of water injestion? I don't have any adverse symptoms other than a lack of power/WOT RPM. The boat always starts right up and idles just fine.

FYI - I put a new set of plugs in the boat after checking the compression a couple weeks ago (wasn't planning on it, but I broke a plug). The new plugs still look very clean after 3-4 hours. I even pulled the plugs directly after letting the engine idle on muffs for a half hour, and they all looked just like the pic in the first post. Would Seafoam in the gas keep the plugs looking so clean?

Oh, and the prop looks brand new. Had it repaired before boating season began this year. Based on the markings, I believe it is the same prop (SS) that came with the boat in 1994.

Water injestion, even just a little under high power, can mess up your air/fuel mixture, and keep you from getting full power! Take a close look at those plugs, any "pinkish" coloring, is definitely water injestion (the beginnings of oxidation, rust!)