I’ts been a while since I ran my Challenger, but I would suggest a starting point of one turn open on the low speed and 1/2 turn open on the high speed. Keep in mind that the low speed circuit is of the air metering type… to go rich, the needle is turned IN,
while leaning the mixture [adding more air] will require opening the needle. The high speed is adjusted the same as all other motors such as OMC’s, etc.
One other bit of advice while adjusting the low speed needle on these motors, is that the motor responds more slowly than say a typical OMC engine would. Make slight adjustments then give the motor time to respond. You will find that carb to be a little finicky,
but if everything’s right, a CC Challenger will idle down to a slow tick. In my opinion, it’s a toss up between my Martin ’45’ vs. my CC challenger on which one will idle the slowest! Great engines!