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Old 05-17-2012, 09:50 AM
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Blown 496 carbon fouling middle cylinders

What am I missing? I have been tweaking the idle on all eight corners to get the A/F at cruise from 12.2 to 13.5 range. I was using #1 as a guide going from light tan to gray as it leaned. I have an intermittent miss at steady speed and the MSD cap and rotor looked pretty crusty so I replaced them. When I pulled the plugs 3,5,4 and 6 were carbon covered and the others look like #1. Wires are all under 200 ohms and cranking compression is 160 on all 8 holes. After 50 miles last night the outer 4 are off white and the inner 4 are off white on one side and black on the other half of the porcelain.
Idle a/f is 12.3 and leans to 15 on light acceleration then will quickly drop in to 11's as I row through the gears. Same on highway.
My set up is:
8.3-1 496 locked 32 timing
420 megablower 1-1 6lb boost
Edel Perf RPM heads
dual 650 dp man ref Holley's QF blocks 9.5 pv's stock ifr
Lunati 114lca 109icl 240/245 @ .050 .647 lift hyd roller
29" tall Mickey's
3.90 gear
cruise at 60 in 4th - 2600 5th 1900

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Old 05-17-2012, 10:57 AM
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Mark the inner plugs so you know the position of the black side of the porcelain to the exhaust valve guide- you may be pulling oil in through the guides.
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