Hi nGuys- I see there's a lot of stuff about carbs here so I guess its a perennial topic! I am restoring 2 CVB250 K4s. Both start and run but both have the same feature- I don't call it a problem yet... the first thing is that for each the air screws seem to be very close to fully in (rich)- maybe 1/2 turn out but thats all and this seems quite close to me. The second thing is that when the engines are warm and I shut them down- both give me a hissing sound- not sure if this indicates a head gasket leak which maybe would account for needing a rich mix but I can't really localise this hiss so I can't say for certain its from the head/barrel join. Also when shut down presumably there isn't anything under pressure any more that might hiss anyway?