sounds like some rich running engines, mine did the same thing after about 10 flts take off the limiter and lean the engine out, or get some help from a more expierenced flyer with some tuning knowledge.
its the toughest part of working on your plane, getting the engine dialed in.
after a little leaning out of the low end and a couple of small adjustments my 46 ran like a top.I did get some help with it also from a couple of club members.