Back around 1997/8 Ivo convinced the owner of Europa Aircraft to try one of the in-flight adjustable props on the mono-wheel 914 powered demonstrator. We put it on just before Sun & Fun, flew it about an hour and were doing ground runups with it when Ivan Shaw (Europa's owner) noticed the tips flexing thru a two or three inch arc on full power runups. He said to remove it, box it back up and send it back. While I thought it was smooth in flight I never liked the foam core (yes the originals were foam C.D.) and really didn't like that much flex in a prop. I know a lot of people swear by them but I am not one of them.
I instructed in a Beaver 550 with a 582 for about 75 hours before the endorsement changes. My rule of thumb was if you didn't dump the nose within a second or two of me pulling the throttle, I would slap the front seaters helmet to wake them up! I would always tell them "things happen fast in an ultralight". The guys transitioning from F-16's and L1011's would always laugh at that until we got up to altitude, banked it over 45 degrees and pulled the throttle to idle. It would usually snap out of the turn in a couple seconds if you didn't release the back pressure. Then they would get it. I would pull the throttle all the time on takeoffs and taught to point it down fast if you want to avoid a crash. Deadstick in the Beaver entailed pointing it almost straight down to maintain 60/65 until you flared, you got one shot at it, maybe, maybe a slight amount of float to help.
Sounds like one of the carb springs might not be working correctly? Maybe when you advance the throttle one carb is "outrunning" the other causing an imbalance? Either way I would go thru the carbs and/or see if you could swap a known good working set of carbs with someone?