sprak plug readings

Terry Stapley · #1 (**permalink**) 02-22-2005, 07:25 AM

Hi Cobra fanatics, I just replaced the plugs in my 418W after 3000 miles. Upon pulling the plugs I found that the back two on the drivers side on the back one on the passengers side were very black and damp. All other plugs were clean and the porcelin part was a chocolate brown. I have been using autolite # 25 plugs. My question is do I need to go to a hotter plug for those three holes or is my problem something else! I had started the engine and let it idle for about 15 minutes to keep everything operating correctly before I pulled the plugs. Thanks in advance for any ideas and suggestions.

RACER X #99 · #2 (**permalink**) 02-22-2005, 02:24 PM

Terry, you could be getting a false reading as that is not the proper way to read plugs. You need to get the car up to operating temp and make some wot runs and then shut down the engine and read your plugs. No idling or cruising back to the garage.
The best way is to get on the interstate if you don't have a ractrack at your disposal run the engine under load at wot at 5-6000 rpms than coast into the rest area and do your plug checks. I think you will find your plugs looking a little different.

Excaliber · #3 (**permalink**) 02-22-2005, 02:35 PM

Solid advice Racer X as it comes to reading plugs, but I would be concerned about the three "black" ones in question here.

As the others are all ready a chocalate brown (not a bad color) under the same conditions as the three, I would have to ask: "Whats up with those three?"

GOT to use the same plug for every cylinder, thats for sure! Plug wires not delivering enough spark to the three perhaps? Assuming compression, valve settings etc are same for all cylinders.

Assume after a good run as noted above, ALL cylinders are now "brown". Will the three "foul" upon idling again? Valve guides leaking some oil in those?

mr0077 · #4 (**permalink**) 02-22-2005, 02:40 PM

Yeah, what Racer X said...it's a bit less user friendly but gets a correct reading for WOT (the most important) conditions. Also, drive the car for 15+ minutes at operating temperature at a cruise and read them to check cruise conditions.

Terry Stapley · #5 (**permalink**) 02-23-2005, 07:11 AM

Thanks for the info and I will give what you suggest a try!
It is almost good enough weather to try out your suggestions!

blykins · #6 (**permalink**) 04-12-2005, 10:42 AM

What did you find out Terry?

Terry Stapley · #7 (**permalink**) 04-14-2005, 07:33 AM

Brent, after a wot run the plugs all looked very good. (chocolate brown). It seems that the three plugs in question only foul up (pardon the pun) at idle!! I already know that it idles a little rich by the aroma of unburnt fuel in the garage!

blykins · #8 (**permalink**) 04-14-2005, 09:24 AM

Yeah, mine's the same way....I'm gonna try a little hotter plug....

bigmike · #9 (**permalink**) 04-14-2005, 11:21 AM

Terry;
Do you have 4 idle adjustment screw on your carb? If so, lean out the closet screw(s). That should help. For more info, go to:

http://www.4secondsflat.com/

BigMike
PS we go rumble, rumble soon!!

Terry Stapley · #10 (**permalink**) 04-21-2005, 10:39 AM

Thanks Mike I had not thought of that! DUH!!! I will give it a try!