Hi Richard
Glad you got to the bottom of this problem, I would love to know exactly what your friend did to cure the problem as I wasn't aware there was scope for mixture adjustment (as has been said). I remember that a 'dribbling' injector or one that is malfunctioning can fail to promote good atomisation at low engine speeds and hence 'deliver a weaker charge - is this what was happening?. Manifold air leaks could cause similar effects as well as vacuum always greater at the same kind of engine speeds.

Hi Giocast
We checked the exhaust with a probe and altered the adjuster screws which are on the right hand side of the bike until we got what my friend regarded as an improvement. He expected a certain level on his readout screen and one cylinder was below par. So we made them more equal in terms of the readout.
RP

Sounds like he adjusted the airbleed screws to achieve the same CO reading for both cylinders.

I agree with above. The screws he adjusted where the air bleed screws.

Just as a reminder, below quote comes from the setup guide that is on this site and the web.

Set the IDLE Balance by adjusting the airbleed screws counterclockwise and confirming that the vacuum is identical for both cylinders at idle. You can rev the engine and observe vacuum tracking through the rev range, and then observe idle vacuum restabilising. NOTE Since the airbleeds are designed to iron out any irregularities in the throttle's function, by their nature there is no default setting, unlike the idle screws on a carburettor. If anything the default setting is fully closed. Airbleeds can also be balanced using a 2 channel CO meter. In this case, just adjust the bleeds until both cylinders have the same CO.
• Adjust the IDLE Mixture. Finally you get to set the CO Trimmer ! This will affect both cylinders by the same amount, so you need to set the airbleeds first. A typical CO figure for idle is 4% to 6%, but automotive regulations usually specify a CO of under 1% to meet emmissions standards. A V-twin will idle very poorly if the CO is set below 1%, so if you are really bothered try a setting of about 3%. Note that you may need to finesse the airbleeds at this stage.