Is the carbon wet (oil fouling) or dry (fuel fouling)? How long since the last complete tuneup?

Try using the extended-nose Autolite 985 or NGK ZFR5N spark plugs and see if that helps.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'm betting the carb is a Holley!

D/W

_________________

If it ain't broke, fix it!

Dan, I just installed and am happy with a set of Autolite 925 plugs, which I found recommended on Allpar.com, thanks to you. The nose and electrodes are pretty long, perhaps 1/4 inch more than stock, so I threaded one into a spare head to see how far they stick into the combustion chamber. I decided it wouldn't be a problem at all unless I were running a domed piston.

Instead of merely noting that they run much better than the worn-out plugs I removed, I suppose it would be a lot more fair to compare them with a good set of regular short-nose plugs. All I can really tell at this point is that the Autolite 925 works fine on a stock but very tired engine.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Good catch. I don't know why I keep typing "385" when I mean "985". The 925 is disco'd; 985 replaces it and is identical in all respects except it has a 5/8" hex instead of 13/16", so you need a different socket to install or remove it.
Wise to double-check this, because yeah, visually, they're pretty extreme. There's tons of room, though.
Keep an eye on them. My experience is that they tend to stay cleaner longer and be more resistant to misfire.

- Erik[/quote]

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Funny you should mention the longer nose plugs? My son and I were just looking at his head last evening and noticed that the plugs are recessed up into the chamber quite a ways. Perhaps 4 or 5 threads are still showing when looking into the combustion chamber. It would appear that this would hinder some flame travel ?? We will have to try the longer tip plugs when we get it back together. How far into the chamber should the plug be? Thanks Dan,

Rick

Ooh, yeah, that's not good for a few different reasons. Sounds like you may not have the right plugs. What year head are you working with, and what plugs are you looking at? The plugs' threaded shank should be exactly as long as the threads in the head.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you are using a pre-'73 head, the kind with the spark plug tubes, please take note.

The new plugs will usually come with washers already installed. The washers should be removed for use with a slant six. I've noticed a real difference in cold starting. It was a notable improvement when I removed the washer.

I've got a spare old style head, and without the washer, the correct plug will end almost exactly at the end of the threads. Even the super long looking electrode is not nearly long enough to hit anything. Shaving the block and the head wouldn't be enough to close the distance. I agree that anything short of domed pistons is pretty safe with the hot plugs.

_________________
1980 Aspen 225 super six

Does power and gas mileage increase when using these plugs? How about idle quality? Does Champion have a similar plug, because that is what my car has in it now.

_________________
82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

If any of these things is significantly improved by putting in a different style of spark plug, it was because of deficiencies in the removed plugs.
Champion makes RN13LYCs, but I don't even run Champion's junk in my lawn mower any more.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan,

The head we have is probably a late 60's or perhaps early 70's head. I bought it in 1978 and I know it had been run for several years before that in a circle track car. The plugs that we have are Autolite 26's and I'm sure they are not correct. They are at least 1/4" from being to the end of the threads. We will have to try some of the ones you mentioned. When we put the engine together, I'm sure I just asked for the plugs for a 72 Dart and that's what they gave us.


Thanks again,

Rick