What propeller are you using?
You may be able to go with a lower pitch to increase the RPM and get more pull.
You can also go with a thinner blade propeller to get more RPM.
You could also not have enough rudder or strong enough servo on the rudder and getting blowback.
ORIGINAL: YSUSER
I have a Quadra 50 and can't get the thing to run right. It always sounds too rich on the high end but will idle great for ever. I have it on a Midwest Exra 300 which is 18 lbs and it won't even hold a knife edge. This engine should be trying to pull the firewall off this thing. Any ideas will be most helpfull.