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We're at the Wendover NT and #4 is not firing at idle. It wakes up at around 3k rpms. Make a run and we come back to the staging lanes on all 6.....idle is up 2-3 hundred rpms and shut it off. Fire it back up for the next run and the hole is dead again. Back to the lanes & it's back on 6. Get back home and a compression test on the hole shows over 200 psi like the rest (+/- 10).
Idle jet is clean, spark seems maybe a bit weak (MSD set-up) but visable spark......
Ideas?

Oh..... 2nd of 13 in XP.:)

JP,

Sounds like a piece of schmutz in an idle passage. I'd remove the idle jet, drain the float bowl, and blow air back & forth several times from the main jet passage and idle jet to dislodge it.

In most cases you never see the offending crud.