RoadVettes

I have a 67 coupe 327/300 and I'm only getting a few hundred miles on a set of spark plugs ( 3 sets this year ) :mad All 8 plugs are covered with black soot (carbon).
The stock carb. was dumping alot of gas into the engine so I had it rebuilt. After the rebuild I drove car to the guy that did the rebuild and he adjusted all the settings.
As soon as I put new plugs in, the car runs great for 200-300 miles then plugs foul again. I tried AC-44 and AC-45. 45's lasted a little longer but not much.
I've gotten real fast changing plugs but I'd rather not do it so often :(
Any sugesstion would be greatly appreciated.

Thanks,
Charlie


[Modified by user9ryan, 7:43 PM 8/16/2001]


[Modified by user9ryan, 10:18 PM 8/23/2001]

Vetterodder

If your car is used like a lot of classics are, i.e., short trips and not many miles driven in relation to the number of cold starts, some carbon is normal. Are the plugs actually fouling and causing a miss or do they just look bad? My plugs usually look pretty dark after a cold start and warm up on choke but look fine after a few miles of high speed running (or a couple 6,000 rpm blasts ).

Another thing to consider is the rest of your ignition system. You could be getting enough energy to fire new plugs but not enough the fire them once they get a dose of carbon (or to burn the carbon off). Everything is fine until the resistance of the plugs becomes greater than the ability of the ignition to fire them.

RoadVettes

Vetterodder,

The plugs are fouling to the point of engine misfire. Hesitation and backfireing on acceleration. Starting and idling are fine.
If it's a weak ignition problem, where would you start looking?

Thanks,
Charlie

magicv8

I can get 5000-6000 miles out of a set of 44S (extended tip) plugs, but be careful if you have domed pistons. I currently have R45S plugs on a Pertronix coil. I wouldn't load down my stock coil with resistor plugs, but aftermarket coils are cheap and available. You might even try 46 or 46S if you do a lot of short or cold weather trips.

Dave62

Ryan,
I had a similar problem wich turned out to be ignition...the motor was not stock..plugs would last 200 to 500 miles depending on how I drove it.
I put a MSD ignition box on it and solved the problem..same plugs for 2,000 miles and still going strong.
If you want to stay stock on the ignition I would replace wires, coil, resistor balast, cap, and points. A bad distributor can cause all sorts of problems but they are usually associated with high end miss.
You also need to check the carb. Rich mixture and or rich main jets can cause the carbon/plug problem but if its really bad enough to cause a problem you should see black smoke.
I would bet its ignition.

INMYBLOOD

Very interesting..... My brother has the same problem with a 402BB Chevelle. It only would go a few hundred miles and then start missing. The plugs would be black. He tuned and retuned but it was it always happend. Eventualy he gave the car to the local "expert" this guy is really a good hot hod tuner. He rebuilt the carb and it seemed crisp but..... It still fouled the plugs. He was so interested he is going to flow test the carb because he wants to know what went wrong. We have always believed he should have pitched this carb but it had a lot of money already in it so he kept trying. It is still out at the "experts" shop so we don't know what the malfunction is yet but it sounds very similar ;) This car has an HEI with an MSD so we do not believe it to be ignition. It will most likely lead to a new carb :jester
P.S. He has a test carb on and I believe it does not foul the plugs.

JohnZ

AC has recently discontinued the "46" heat range, and now shows "45" as the substitute. For cruising duty where a lot of our cars tend to carbon-up the plugs with rich performance carb jetting, there are several other brands that still have plugs in the heat range equivalent to the discontinued AC "46":

Champion J18YC (projected tip, non-resistor)
Accel 0138 (projected tip, non-resistor)
Denso W9P-U (projected tip, non-resistor)
Autolite 76 (projected tip, non-resistor)
Autolite 86 (standard tip, non-resistor)


[Modified by JohnZ, 11:46 AM 8/17/2001]

66c60

over the past 30 odd years i've used ac-44 plugs as recommended by chevrolet. when the plugs got sooty or oily i fixed the engine or carb problem. going to a hot plug is not a fix.

SWCDuke

Hotter plugs are the way to go. The AC44s recommended for SBs for "town and country" driving are too cold. My SHP engine would build up deposits and misfire - not carbon, but lead oxide. AC45s went a lot longer before fouling. There was nothing wrong with the engine or carb.

Duke

magicv8

The last two times my plugs went black in a hurry, my wires were at fault, and replaced under lifetime warranty.

I have read and repeated: 90% of all fuel problems are ignition problems.

My carb hasn't been a problem in ten years. but the plugs turn black when the wires go bad. If the back of your car is black or dark brown, fix the choke or rejet the carb. :smash:

RoadVettes

Thanks guys for all the sugestions.
Today i put in new plugs (Champion: RJ18YC ) and replaced the coil, it looked pretty old. Wires are almost new and the car always runs great when new plugs are in, so I don't think the wires are a problem. Tomorrow I will pick up new points. condensor, and ballast resistor.
INMYBLOOD let me know what your brother finds out about the carb, I'm still not sure that this isn't a fuel problem.
Hopefully one of the above will solve my problem, but I guess I won't know for a few hundred miles.

Thanks all,
Charlie

67 Marlboro Maroon Coupe
:chevy

Vetterodder

Charlie, it may be possible that what's causing the backfiring and hesitation is also causing your plugs to foul and not the other way around. (As far as I know, the chicken/egg thing is still a mystery ). Your symptoms are not normal and, obviously, there IS a problem. The possibilities are numerous and, without seeing/hearing, the best we can offer is it might be this or that. The other posters have given you excellent advise. It could be a screwed up carb, a faulty ignition component, a valve train problem (broken or weak valve spring, bent pushrod, slipped timing chain, etc.), a gasket leak, or something else. In any case, the problem isn't going to fix itself. Try the simple things (and most probable/inexpensive) first. If that fails, take it to a pro but not the same one that couldn't fix it before.

magicv8

The cost of points, condenser, and ballast resistor should be put against a Pertronix ignition set that replaces all 3 with (in my experience) a very dependable package that fits under the distributor cap and requires no periodic maintenance (ever). I got mine through a sale catalog from JCWhitney years ago. It removes a lot of variables.
:seeya

6T5RUSH

User9Ryan,

Just stumbled accross your dilemna.

I'm experiencing the same thing you are only it's on the #1 cylinder. I'll go 300-500 miles on new plugs (R45S), and she'll develop a miss...no backfiring, detonation. It's got so I'll just pull the #1 plug, see it covered in black soot, replace the plug and she's hummin'. What's up with that? I should mention that when I pulled all the other plugs, they would all be black, but still firing. Wouldn't this point to too rich of a mixture...carb? Why then would it take out just the #1 plug? Does the #1 get a little more fuel than the rest of the cylinders???

Like you, I'm getting good at pulling plugs...it's just a pain pulling all the ignition shielding away to do this.

Jim

RoadVettes

Jim,

My plugs are all carbon covered about the same. If your #1 is alot worse you way want to check that wire, not enough spark won't fully burn off the fuel.
I'm still not sure if my problem is fuel or ignition, but Saturday I put in new plugs and a new coil and put about 100 miles on Sunday going back and forth to a local Vette show (took a 2nd place trophy :D ) and she ran absolutely great. Hope to put more miles on after coming back from Carlisle, and then I'll pull a few plugs and see how they look. Hopefully the new coil will make a difference. I'll keep you posted.