I think your idle is set a bit low. I think the spec is 600 RPM in gear. In neutral that might be 800-850 RPM. I'd try that. The increased RPM will help increase the vacuum signal in the carb...maybe.
A bog off idle usually indicates a fuel starvation issue. It wouldn't hurt to back the idle mixture screws out 1/4 turn. 19" of vacuum is PLENTY. my build runs at 10-11" and powers my brakes just fine.
I'm a hobbyist. Not a professional. Don't be hatin'!
