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well if he said 18ft ..that is very good air.. I would not call it mineshaft air but very good. And if you run in 2000-3000 ft da..That is alot of change depending on how your car was jet'ed to start with. It could be very lean and to add to that a headwind would make it leaner on top of that. one anytime you add load to a car it lean it and head wind pushing more air in the scoops.

You would normally jet down for bad air such as hot summer days and jet up for good cool dry air of spring and late fall if you were lean to start with then the good/mineshaft air would compound the issue and cause the miss problem, altho I do agree with a lot of the other suggestions that the guys have brought up here as possible reasons,, but I have also had a friends car that has experienced a high speed miss when the jett is too lean for the conditions like weather change's and we have to jet it up.

Light travels faster than the speed of sound,,,this is why some people seem bright untill you hear them speak.