the computer is messing with the timing/spark tables. You could try to lock the timing out nd run without the spout in...or get something to control/replace the computer. I happen to have an A9L conversion harness with computer and BAP sensor for sale
As SQUEEZE&STROKE said, the computer is messing with the timing/spark tables. It advances or retards the timing as it deems necessary. What's your base timing set to, with the spout connector out? Most people can't run more than 14° of timing without problems.