What I'm up against on tuning the SS800 using the Gunson CO tester, mercury manometer, and IAW reader/writer program:
Synchronise the Butterflies:
• Close the air bleed screws completely by adjusting CLOCKWISE. If you don't do this then the throttle vacuum will still reflect any air passing through the bleed channels and the butterflies will not be perfectly synched.
• Attach vacuum gauges to the manifold port on each cylinder and run the engine.
• Adjust the throttle butterfly link shaft until vacuum is identical.
• Rev the engine and confirm that vacuum tracks on both cylinders throughout the throttle and RPM range.
• Re-adjust the link shaft until satisfactory results are obtained.
• Do Not adjust the throttle link shaft after this point!!
Set the IDLE Balance by adjusting the air bleed 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 re-stabilizing. NOTE Since the air bleeds 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. Air bleeds 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 air bleeds 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 air bleeds at this stage.
Adjust the IDLE RPM. Set the idle rpm at the manufacturer's figure (usually 1100 - 1200 rpm) by adjusting the throttle butterfly stop screw (or screws). We recommend 1200 rpm for Ducatis and Guzzis, possibly 1500 rpm for Ducati 996SPS models.
Finally, note that the last three steps are usually repeated until an acceptable balance of Idle Balance, Idle Mixture, and Idle RPM are obtained. This is normal. Do Not adjust the throttle synchronization link shaft once it is set in the early stages. If you do this now, you will need to go through the entire sequence again.
So hopefully you will have an engine which now idles, accelerates, and delivers full power faultlessly. Again, if you are not confident about all of these steps, then we suggest you use a dealer who has the skills and equipment. It is not worth adjusting the CO trimmer unless the entire sequence is followed without skipping any steps.
Admittedly, I didn't follow the above (superbly written) guide in my prior attempts, though I achieved a certain success in doing.
My springtime (next) attempt should achieve much better results using the Gunson meter with the special tool I have fabbed.