Quote:
Originally Posted by Stearman
Remember, you can only get rich indications or heavy black carbon deposits AFTER the fuel mixture is ignited. So, if a black fuel rich "soot" was inside a runner...that means an intake valve would be hanging open after the mixture was ignited and through the exhaust stroke.
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On family car engines, this reasoning is good, however it depends on the cam. If there is a lot of overlap on the valve timing, the intake valve opens at the end of the exhaust stroke. Exhaust gasses do enter the intake at idle, which is why the manifold vacuum is low.
My cam is 236 deg intake and 242 deg exhaust at 0.050" lift. Exhaust carbon is all the way into the plenum on a Victor Jr. Single plane intake. I have EFI so there are injectors drilled into the ports. The fuel washes some of it away, as the carbon is heavier before the injectors. If it was a Carburetor, the fuel may wash some of it away. When I pull the throttle body, it wipes off with a rag.