how can i fix aprilla sp 50?

The radiator hose was leaking, so i took hose off and put new jubilee clip on.
all water came out so i filled it up and bled it.
after that it would start but ran rough then packed in we have changed plug but it does not idle.but now it runs sometimes 10mls and other times it wont even run for a mile. it is now at aprilla agents,they have plugged into computer but it wont pick up fault.can someone help my son is driving me mad.the usual always dads fault

regards

jeff