Finialy got the engine timed right and ignition system working correctly, but I had the carb rebuilt and it won't idle, even when warm without the choke. My carb is a Carter W-O. I have it set for 600 RPM idle with the choke. I have the A/F screw 2 1/2 turns out. My first guess would be a vacuum leak, but I couldn't find or hear any. The float is set right. The exhaust smells like the A/F is correct with the choke. Should it have a rich smell when idling? and then a neutral smell without the choke? Engine is a fresh rebuild, done be a local professional engine building shop.