Spark Plug Reading/Evaluation
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Spark Plug Reading/Evaluation
I pulled my plugs today on my 1978 F150 (carbureted 302) and this is what they look like. The porcelain is white, but the ground strap and the base it attaches to has soft, sooty deposits that will rub off with your finger. Is this normal for a carbureted engine, or is this a bit rich?
Postmaster
Joined: Mar 2011
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From: Taxachusetts
Yes, she's running rich. Have you used a vacuum gauge to set the mixture?
Reasons, (could be): plugs are too cold, jets are too big.....can't tell if your timing is ok - the pictures are bit fuzzzy - hard to tell a few things.
Reasons, (could be): plugs are too cold, jets are too big.....can't tell if your timing is ok - the pictures are bit fuzzzy - hard to tell a few things.
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I pulled these right after a 45 minute drive, mostly 45 - 65 MPH, and then less than a minute of 5 MPH driving into my backyard and idling.
I adjusted the timing and mixture screws using a vacuum gauge. The engine seemed to run fine, but I had a very strong gas smell, and the exhaust pipes were CAKED with carbon buildup, so I then checked the spark plugs. That is when I discovered they were completely covered in soot.
I jetted down two sizes from there, and the plugs cleaned up nice, to what I now show in the pictures. Should I reduce the jet size again? All 8 of the plugs look about like this one.
I adjusted the timing and mixture screws using a vacuum gauge. The engine seemed to run fine, but I had a very strong gas smell, and the exhaust pipes were CAKED with carbon buildup, so I then checked the spark plugs. That is when I discovered they were completely covered in soot.
I jetted down two sizes from there, and the plugs cleaned up nice, to what I now show in the pictures. Should I reduce the jet size again? All 8 of the plugs look about like this one.
Cargo Master
Joined: May 2009
Posts: 2,587
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From: Eagle River, AK
The process of reading plugs is pretty involved and you will skew your readings by idling before shutting the engine down.
There are specific steps for reading the plugs when different circuits of the carburetor are being utilized.
There are specific steps for reading the plugs when different circuits of the carburetor are being utilized.
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
With that said, I would try a hotter plug before anything else......and time your motor again with a timing light! I've said it before and I'll say it again - a vacuum gauge is for diagnosis and tuning the carb. Period. A timing light is used for TIMING the motor. Would you use your timing light to to fine tune the carb?
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