It could be several things. do you have a setup manual??? They are £6.99 on line from dellorto. Or look here for the basics.
http://www.scribd.com/doc/9641108/Dellorto-Manual
Is it the correct jets for the bike or a guess??
What you describe sounds like not enough cutaway, ignition timing or too rich on the needle. It depends on the throttle position and load on the engine.
Choppling isn't hard, I do it but it can be time consuming. I get the bike right by feel to start with then chop as a check.
The Amal system is to set the main jet, set the pilot jet, set the cutaway, set the needle jet and position then recheck the pilot and set tickover. This is done purely by feel and not by chopping. They give tips as to what to look for.
