Variable spark plug conditions ... normal? (1 Viewer)

Joined
Jul 18, 2020
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Boulder, CO
Changed the spark plugs today on my ‘84 FJ60. It’s just one of many little things I’ve been doing in the last month or two since I bought it to know that you the details are taken care of. I notice that the plugs toward the front of the engine were running hot, while those at the back were relatively normal. Is this a common situation with these engines?
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Joined
Aug 30, 2009
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Steamboat Springs
I've found that before on 2F's. Performed Lean drop tune on the Carb, checked the timing, full tune up of the motor and still have that happen. possibly due to unequal fuel distribution to the cylinders ?
 

OSS

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Jun 30, 2017
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Oblivion
The front plugs will always stay cleaner than #4 and back. At least mine always did from 36K miles (2 year old engine) to 292,000 miles (30 year old engine)
 
Joined
Jul 18, 2020
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Boulder, CO
Interesting thanks. And I forgot to mention that I have a Weber 32/36 carb on this motor, not OEM.
 

Seth S

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Jan 4, 2011
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The conditions in the intake manifold and exhaust manifold are a lot more complex than most people realize. Its not as simple as air flowing through the carb and air/fuel flowing into the cylinders and air flowing out the exhaust manifold. There are all sorts of pressure pulses and sound waves and flow turbulence and general chaos in there that affect how much fuel and air each combustion chamber gets. Also the distance from the carb to each cylinder and from each cylinder to the exhaust manifold exit is different. So essentially without things like EFI and tuned manifolds you are going to get more variation in how each combustion burn occurs.
 

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