I finally had time to run the Echo last night. Had a problem with the carb so I swapped in a "stock" Walbro of the same size. With the ignition fixed at 12-13 degrees advance I could get a decent idle and 6300 rpm on a zinger 14-8. I'll try to get more advance and find a happy compromise of idle/top end.

You're right, this is a small motor.

I was test running it with a 1 oz fuel tank and got 4-5 minutes of fiddling with carb needle settings and running it up and then idling. I'm thinking a 4-6 oz tank will be enough.