Idle speed and tach

[BRIELLY]

Well I finally got the bottom of my engine troubles. Upon rebuilding the carbs I found the bottom one was completely gummed up. I got them back together fired it up and it was idling very high. I turned the speed screw and got it down but now its running rough. I may need to mess with mixture next but the real problem is I have no idea what rpm's its currently idling at. I tried a multimeter with tach attachment but got no reading. I have an older style automotive tach with alligator clips but I have no idea what to hook it up to to get a reading. Can anyone tell me where to connect it? Thanks!