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This right here - Before you pull your head, rebuild this puppy. Then Seafoam your engine. A carb that runs rich will deposit loads of carbon on the intake & exhaust valves. Carbon can also get really hot and then it'll act like a glow plug in a diesel - you'll get misfires or knocking. Seeing as how you heard the leakage from intake & exhaust rather than leakdown, you might just need a deep cleaning after returning to a normal AFR. Run Marvel's mystery snake oil in your next few tanks of gas. The rest of the carbon will burn out over the next few weeks of driving.Another thing, if this carb is toast, it may be time to gut the MCU system and put a non-feedback carb on. I see I-6 F150s used the YF carb as well as some cars from the late seventies. Will any of these bolt up and work ok? I'm not after performance, just something that will be relatively easy to set up and then will stay that way without requiring constant fiddling.