[Zeke's Garage]

Do you hear the secondaries open when it's bogging? Also you say that if you get off the gas, and ease into it, you can get it to go up to 70+.

Sounds like the jetting is too rich on the secondary metering rods when the secondaries kick in. I think that if it couldn't get enough fuel, you'd get lean backfire through the carb as it was running out of fuel.