View Full Version : Spark plug color????

04-06-2005, 09:27 PM
Tuning in my freshly rebuilt Stromberg carbs so I went through the entire electrical part of the tune up, adjusted valves and put in brand new plugs. After setting the carbs where colortune told me, I went out for a spin. One and two cylinders show a very slight rich mix with very light soot on the plugs. Cylinder 3 plug reads a perfect mix but cylinder 4 reads way too rich with soot. Compression is 155-160 in all 4 cylinders so I don't feel it's burning oil in #4. Any idea why #4 has so much soot on the plug after a 10 mile run?

04-06-2005, 09:36 PM
TR4, My guess, valve guides, just worst in #4 and you have more oil pressure there, so more oil flowing in that area. OR, it might be as simple as bad sparkplug wires or coil. Wayne

04-06-2005, 09:44 PM
I second Waynes thoughts. Very often valve guides when they get worn will allow enough oil into the cylinder to make your mix look too rich. I wouldn't worry about it. I wouldn't think it was the coil, since you say number three looks perfect. It wouldn;t hurt anything though to double check your plug wires, and even the connections under your distributor cap.

Geo Hahn
04-06-2005, 09:57 PM
Any idea why #4 has so much soot on the plug after a 10 mile run?

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I'm not sure a 10-mile run in Ohio in April is going to give you and accurate plug read. You may have even spent some time on the choke -- I would check again after a long drive.

04-17-2005, 08:42 AM
Well Mr. Hahn, as they say in the UK, you were spot on with this one. We finally had a 70 degree sunny day here in Ohio so out for a 50 mile loop in the TR4 and all 4 plugs are reading proper air/fuel mix. The choke must have caused my unwarranted worries. All systems go for the driving season. Thanks for lending your advice to this newbie LBC owner. I owe you a tall cool one.

TR4-Phil /ubbthreads/images/graemlins/cheers.gif