Could not figure out how to put pictures in the mail.
Overall of the carb:
Close up of the fitting;
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Have seen another saw with a fitting and line down through the case. IPL shows a line from the CARB into the lower case.
Hal
OH yeah I have been working on a bunch of these lately. With this setup, the carb has no idle screw that opens the throttle. Instead the idle is achieved by dumping air into the crank case. Not sure how but somehow the carb still feeds gas as well, I guess because it is still getting pulses. The fitting on the manifold is just for the idle screw. There is no connection to the mixture coming from the carb. There must be some sort of check valve where the air enters the crank case to prevent backflow. Maybe "crank" ported, as opposed to piston ported. Often the carb is swapped out for a HL with a set screw, and the crankcase inlet is blocked off. I know with the extra idle circuit, it is much harder to take it apart and work on it.
I can see that you have the idle screw on the carb, so the other idle circuit is inactive.