Technical > Spud Miller's Cave

Main jet vs idle mixture

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BK:
 When I change my main jet I need to adjust my barrel valve the opposite to maintain idle mixture. Is that normal or am I missing something? I have a smallblock Chevy around 500hp. Hilborn O pump a set of your Enderle .028 flowed nozzles, Enderle cube barrel valve, 5lbs idle pressure, Bypass ends up around a Kinsler .085.

Spud Miller:

 Yup, that is normal. One should never adjust the main pill to change the idle, but changing the main pill WILL raise and lower system pressure a little bit at idle and cause a change to the leakdown percentage required.

 Generally, if you're over .100 on the main pill, a .005 step won't require a tweak to the hex-link. But two or three .005 steps will need an adjustment...usually just a flat or two.

 When the main pill gets LARGER, idle fuel pressure will drop a little and make the idle a little lean.

 Spud

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