Suggestions for non-Magnum 360 that started running badly?

One day I went to start up my '62 Valiant resto-rod with a non-Magnum 360, and it had a huge miss. Wouldn't idle. It will run if you hold the RPMs up, but still seems to have a miss.

I've squirted carb cleaner into the idle jets and carb throat, with no improvement.

Sure would appreciate it if you guys would suggest some other things to check.

Thanks very much.