dirty, carbon-covered spark plugs - what's the cause?

[Happy Face]

Recently my car has been running and idling rough. Since I've never changed the plugs I decided it might be a good time and I bought some NGK plugs. When I removed the old plugs they were very dirty, carbon-covered, very bad looking. I figured well, that's the problem, these plugs have had it. So I put my new clean and shiney plugs in, attempted to start the car (It did not want to start), and managed to get it to run after several tries. It sounded like one or more cylinders were missing so I pulled one of my new plugs back out and low and behold its as dirty as the old plugs were! They had only been in there 5 minutes!

So, now the car runs very rough, I'm sure its missing (although I rechecked all the plugs to be sure they were in all the way), and the new plugs are as ugly and dirty as the old ones.

For the hack mechanic, what's the problem here?

[jgerry2002]

Have you changed cap, rotor, inspected your plug wires, and coil? Also check carb operation, especially choke flap to make sure you are not in too rich (lack of air) condition.

[Rob7502]

Did you gap your plugs? They do not come pregaped. The gap should be 0.025". That would cause your car to be hard starting. Noe the reasib that they are so black after just a few minutes is that all that hard starting loaded the cylinders up with fuel so when it did start it was in an overly rich condition.

Now I am jumping to conclusions here but since you have not ever changed the plugs you probably have not changed the wires rotor cap or points. Any one of these can leaf to an engine that misses.

Good luck

[Happy Face]

ok, I changed the plug wires to some nice, heavy-duty red ones I got through Ireland. Had to take the 'tips' off the plugs as the new wires are set up to lock onto the threads on top of the plugs.

I did not regap the plugs because it was my understanding that they were pregapped at 0.030, which I was told was about right. I could remove the plugs again and regap to 0.025.

In any case, after replacing the spark plug wires, the car is running much better. It still has a hard time idling, but will after 5 minutes or so at 2000 rpm...then it settles down and will idle (not as smooths as I would like).

I had bought the new plugs and wires as part of my plan to install a Crane ignition system. I just decided to jump the gun a bit today and put on the new plugs, hoping it might help.

[Rob7502]

I would regap the plugs, I have seen many plugs come "pregaped" only to find that they have a 0.010 varience between them. Also when dealing with as many factors as you are with combustion close is not close enough.

[Chris_B]

which plug are you running (specific model no..)?

[ferrwrench]

Take a step back and think about it.. if you change to new plugs and they foul, then you switch to new wires (old wires will usually only show a no fire or misfire stumble situation) and no change, lets assume you have also changed to a new cap and rotor, since you're in there already, (but unless your cap and rotor are complete crap, probly not the issue, and won't crap plugs that fast..) whats next...what causes carbon fouled plugs? (not the only cause, but a major one)..... especially that quick. an overly rich fuel mixture. What kind, size of carb are you running? Does the choke operate like it should. Is the air/fuel mix right? if so, when was the last time the carb was rebuilt? What is the float level, air passages in carb clogged. If unsure how to setup the carb and adjust the choke, check in the archives, there should be many answers. there are some baseline adjustments, you can do quickly, air mix screws (turn in till they seat, lightly. then back out 2 turns, as a start. if unsure about the choke you can disable it, chokes aren't necessary, they just make life easier. it takes patience to learn how carbs work. There is a lot of good books/articles and posts that explain it, but the best way is to get someone to walk you through it in person, or good ole trial and error. It took me the better part of two years to master 6 twin choke webers on ferrari V12's(which by the way never ran on chokes, the fuel dump is death for cylinders, it washes the walls down.) But when you get the hang of carbs, i'd take them over F.I. anyday,(never will understand why tii are so desireable..sorry tii guys..I love the sound of carbs..good luck

[esty]

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helpful link

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[Happy Face]

mine definately looked like this....although they also smelled of gas...

but that might have been from all the failed attempts at getting car started...

the possibility of a carb issue seems probable here.....oh boy