Yeah guys some real little gremlins here. Lots of little things seem to have an impact. Have had a couple recently and resolved alll but one so far (Yeap thats you Mr Wryt!!!) Nothing I can even suggest off the top of my head. Feal trims and setting spark advance on diagnostic tool helps alot of you still have the O2 sensor, if no O2 sensor then set fuel trim with Co meter. Then balance throttle bdies. Make sure the CO is checked in the header, then engine is warm and is between 3.5 and 4.00. This is pretty important. You can then also take the bleed crews out to about 2 turns is nice, then set the trim on diagnostic tool to reach your required co level.
I have had good results with this method. Those bungs on the side - man really importnat and not to be overlooked.
Hops this helps in some way.