Rpm keeps flucuating at idle

[mother$hip89]

I'm finding ​it really hard to tune the mixture screws as the engine speed keeps moving up and down while idling, almost like it's revving but lightly. This makes it impossible to tell exactly when the screw affects idle speed and vacuum. It is running with the idle speed screw all the way out so I know it is actually running on the idle circuit and not primary. It idles around 800rpm and has no obvious vacuum leaks. Any ideas on what would cause this.

[Cliff Ruggles]

You have a vacuum leak someplace or a LOT of timing at idle, or a little of both.  With the idle speed screw backed all the way out, the engine should not be able to run at 800rpm's.

It would help if more information were provided, engine specs, carb number, what's been done to it, etc?......Cliff