Idle issues when in gear

The problem is not a failure to use lead substitute, so don't fret (or spend) about that. The problem is likely electrical/ignition- or fuel-related, and the mentions of valve lash are wise, too. Follow tune-up parts and technique suggestions in this post, do a careful valve adjustment, and Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.