Sooty plugs and some trace of fuel in oil


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By Nat Santamaria - 9 Years Ago
Hey all.
I have a 312 in my 57 tbird. My 2 front plugs are bit sooty, the next 2 are bit whiter and the last 4 are textbook grey. I am noticing some fuel in the oil pan and I noticed some black thin oil dripping out of the downdraft tube. When I wipe the dipstick I am noticing a bit of black deposits in the oil. I just did the heads in July. The compression is 150 in all cylinders. Leak down test was also good. Vacuum is a steady 18.5. Car runs very smooth. I noticed when I take a temperature reading at the exhaust manifolds the 2 front cylinder readings are in the 390 - 395˚ range. The last six cylinders are 100 -125 hotter. Is it normal for the front cylinders to run that much cooler. Is that the reason for the slightly fouled front plugs & fuel not being burned fully? Valve lash has been checked several times and are good. Could this be a carb issue? I have 4160 that has been on the car for 6 years and maybe 20,000 miles
Float levels in carb also good (just below sight hole)- I am running a Pertonix ignitor and a MSD Blaster coil with the stock resistor. Any help or advice, help or tips would be greatly appreciated.
Thanks all
By speedpro56 - 9 Years Ago
I have seen the front cylinders run a little richer as well, could be nature of the beast. What size is the 4160 carb, what timing are  you using? I like around 12 degrees with vacuum unplugged. Carb jetting could be an issue as well, sounds like a little tweaking is all you really need.
By Nat Santamaria - 9 Years Ago
I am running at about 10˚. The stock Holley 4160 carb is 465 cfm. Jets are 122-57, power valve 8.5
I have the original carb that came with the car 4150 - its a 390 cfm - I may consider rebuilding that one as well. The car ran great with that carb however the it ran very rich in the right bank could not fix the problem.

Thanks for your response
By charliemccraney - 9 Years Ago
Is the vacuum port at the back, driver side of the manifold plugged?
By Ted - 9 Years Ago
Nat Santamaria (2/3/2016)

.... I noticed when I take a temperature reading at the exhaust manifolds the 2 front cylinder readings are in the 390 - 395˚ range. The last six cylinders are 100 -125 hotter. Is it normal for the front cylinders to run that much cooler. Is that the reason for the slightly fouled front plugs & fuel not being burned fully? ...

It’s not unusual for the rear exit exhaust manifolds to show a warmer temperature at the back of them versus what’s indicated at the front.  This is simply due to the accumulation of heat from successive exhaust ports as the exhaust travels from the front to rear.