Plug color doesn’t match the tailpipe

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Plug color doesn’t match the tailpipe

Postby pcguy » Sun May 05, 2013 3:32 pm

Have an odd situation with the built 350 in my 75 Vega - the appearance of my spark plugs ( photo below ) seems to indicate the engine is running lean, but the tailpipe is sooty and very nearly black. Also, the threads on the plugs are wet – before you say it’s the valve cover gaskets leaking, read the following which makes sense to me.

“While it may look like dirty oil, it isn't, this is unburned fuel that all the lighter elements in the fuel have boiled off leaving the heavier hydrocarbon components behind. This is not unusual to find even on race engines. I wouldn't have known this myself if I hadn't run across the explanation from a very respected pro engine builder on another site. This "fuel" is here because the seal(tapered seat or gasket) is above the threads but the threads themselves are shielded from the actual combustion process. Almost sounds crazy but it is true.“

The likelihood that the wet look is from unburned fuel also seems to contradict the lean situation that the appearance of the plugs indicate???

Image

Any thoughts?

Many thanks,
Nick
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Re: Plug color doesn’t match the tailpipe

Postby chevyart » Sun May 05, 2013 11:00 pm

can you turn the plug the other way so we can see the view looking down art
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Re: Plug color doesn’t match the tailpipe

Postby BillPappy » Sun May 05, 2013 11:47 pm

Art wants to look at the porcelain inside the spark plug. As Do I.. Can I ask what octane gas and base timing? Nevermind I found your post stating my Qs.
If your engine is running lean to the point of a lean misfire in a cylinder it will send the unburned fuel into the exhaust just like an incomplete burn of fuel in a rich condition.
Looking down in the plug should show deposits of this. this plug looks like it got really hot to me
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Re: Plug color doesn’t match the tailpipe

Postby pcguy » Mon May 06, 2013 9:07 am

The grounding strap is all the same color which, as I understand it, means the plug is too hot. The porcelain is the same color all the way down and shows a very few speckles of what looks like aluminum – in concert, it appears my timing and the hot plug may be what’s going on. What do you think of retarding the timing as a starting point – I have observed no knocking, even with hard accelerating???

I can post another pic if you need one.........
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Re: Plug color doesn’t match the tailpipe

Postby BillPappy » Mon May 06, 2013 12:06 pm

Deposits of aluminum is a sign of pre ignition. Don't always hear it. At best would sound like a tick rattle with quiet mufflers. If you're knocking TO Hot..
Holley Carb? If it was me I would try a fatter power valve. Richen it up 1 number. I may or may not lower timing. I would try higher
octane gas 1st :) then look at the plugs
Art and a few other here are good at tuning them carbs. Might want to wait for them to chime in :th:
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Re: Plug color doesn’t match the tailpipe

Postby chevyart » Wed May 08, 2013 6:15 pm

best advice i have ever seen is at this site. i have a copy of these 4 pages, but dont know how to put them out on our site. so go here and you will learn stuff as i did about reading the plugs. here it goes. http://www.angelfire.com/fl4/pontiacdud ... plugs.html good luck art
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Re: Plug color doesn’t match the tailpipe

Postby chevyart » Wed May 08, 2013 6:21 pm

that site didnt post right. here it goes http://www.angelfire.com/fl4/pontiacdud ... plugs.html that is a capital R in word Read. all you guys should take a peek at this article art
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Re: Plug color doesn’t match the tailpipe

Postby chevyart » Wed May 08, 2013 6:25 pm

still wont post right. . from here it reads fl4/pontiacdude 428/Readplugs.html
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Re: Plug color doesn’t match the tailpipe

Postby BillPappy » Thu May 09, 2013 3:10 am

It works on my side. :) Info on this page is the best I seen. Should be saved for others.
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Re: Plug color doesn’t match the tailpipe

Postby pcguy » Thu May 09, 2013 9:09 am

Link works for me - actually saw a page that looks like a copy of that page, or at least it was very similar. I have created a list of possible causes of what I'm seeing and my first two changes will be to the timing and one step cooler plugs. The latter because the ground strap color change being very near, if not at, the base ring.

The timing looks like two issues - too weak springs in the mechanical advance and perhaps likewise in the vacuum advance. For starters, I will temporarily remove the vacuum advance and see if the issue disappears.

More to follow....
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Re: Plug color doesn’t match the tailpipe

Postby chevyart » Thu May 09, 2013 4:39 pm

hey billpappy for some reason, my computer wouldnt let me type correctly last night. you seem to have been able to put my posts together to get to that site. can you post that info correctly and maybe get it into the right place for our members to see. thanks art
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Re: Plug color doesn’t match the tailpipe

Postby 80 MONZTA » Thu May 09, 2013 6:51 pm

chevyart wrote:best advice i have ever seen is at this site. i have a copy of these 4 pages, but dont know how to put them out on our site. so go here and you will learn stuff as i did about reading the plugs. here it goes. http://www.angelfire.com/fl4/pontiacdud ... plugs.html good luck art

Your link works fine for me Art, just click it and it takes me right to it.
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Re: Plug color doesn’t match the tailpipe

Postby chevyart » Thu May 09, 2013 9:50 pm

hey 80monzta now i just click on to the blue writing on your post and i am right on that site. that bit of info really shows how to read plugs. art
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Re: Plug color doesn’t match the tailpipe

Postby highstrungvega » Thu May 09, 2013 11:56 pm

My initial thoughts are you are rich but have a real hot plug which is burning off all the residue off the tip. Put an emissions sniffer on it and check the hc's and nox. Hc is hydrocarbon (unburnt gas) nox reading us usually a hot/lean mix.
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Re: Plug color doesn’t match the tailpipe

Postby pcguy » Fri May 10, 2013 9:47 am

That could be, haven't testted the HC's and I suppose that's coming. Have actually drilled a small hole in one of the secondary buterfiles just to prevent that. The power valve is a 4.5 meaning that it won't open until I really get on it and the 66 jets are one of two of Holley's standard sizes - 65-66. Engine seems to run they way I would expect - also though, it does run a little hot (temp).

Have just changed to colder plugs - from R45TS to R44TS and have a whole list of stuff that I need to do/check. First test will be to put it on the road with the new BFG TA Drag/Street Radials.

I definitely will post my results on this - might take a week or two.
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