Gordo,
The popping is from a too lean condition which is a common problem with EPA bikes.

From post #168

Results: The bike pulls better and revs higher. Was stumbling at high RPM before change.

Stock main is a 88. I used a 100 for the first try. Also have a 105 and a 110 maybe to try.
Stock pilot (low speed) is a 40.

Jets from http://www.jetsrus.com/a_jets_by_car...4-36_main.html

Also I installed two washers under the needle that helps the mid range.
Three washers were too much.

Bike pulls much better now and almost no popping.

Still waiting for the 14 tooth front sprocket which should fix the getting across the intersection without shifting to second gear issue. If the sprocket is too big then smaller rear is the cure as suggested by Aboshi.

The above is about what I had to do to my other bikes to solve the lean and gearing issues.