Zenith Idle Mix Screw Doesn’t Kill Engine

[Jim16A1]

Hello all,

I’ve been trying to tune a friend’s Zenith and eliminate the stalling while stopping feature. I found that the idle mix screw seems to have no effect on the idling of the engine. I can screw it in all the way, and it makes a really loud sucking sound, but the engine doesn’t die. I’ve had the carb apart several times and it looks immaculate inside.

Thanks in advance.