Morning vs. Afternoon Jet Changes

[RacinRich]

Assuming a 10-20 deg.F temperature change from a morning track session to an afternoon session, what 12A Nikki carb. jet changes does anyone make due to the temperature difference?

[joeg]

Not sure if anyone makes jet changes in those conditions. General rule (I think) is if it gets hotter, you would go one step leaner --because warmer air packs less oxygen than cold air.

Whether such a temp change requires one step (or half a step or no step, etc) is a question I could not answer.

in so cal its more like 30-40 degrees between am-pm, practice at 7:30 65 deg, race at 3:00 100-105 deg.
nor cal is not so bad, humidity changes are the hard to predict aspect.

[bcarter]

We aren't allowed jet changes, but temperature plays a huge part..

This weekend was our last, and it was cool. On Saturday night it was about 10 degrees C, which is about 50 degrees F.

My best time until then was 1:32.05, and I turned 4 consecutive 1:31's in the race, best time 1:31.22. Why? Not my driving, for sure...it was the cold air. Dead stock carb, rebuilt by Yaw.

Also used more fuel.

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta