Exactly why!
Thats exactly why i put the NB piece at the foot. Exhaust gas analysis.
With carbs you are adjusting the idle mixture and there is NO lambda sensor to screw things up for you. but with the 'Moronic' system you are only adjusting the amount of air able to 'by-pass' the throttle plate and not the idle jet and air bleed. The 'Moronic' and the lambda take care of mixture or rather quantity of fuel injected, hence why it so important that the throttle plates are synchronised to move exactly as one together.
Interestingly enough no matter how many cylinders your engine has there is only one lambda sensor (yes I know some cars have two - one either side of the cat but not on bikes...yet.) therefore the ECU acts on combined cylinder information, which means if one cylinder is seriously rich - example the left throttle plate is open slightly more than the right giving more air flow to the left cylinder and insuffucient to the right ending up with the lambda sensor telling the ECU via voltage output that the system needs a weaker mix/injector pulse width reduction. Result = even leaner mix and hesitation, pinking and general rough running.
Its just a cheap way of satisfying EU emission regs by monitoring total cylinder effect rather than individual cylinder performance upon exhaust output.
The air by-pass screws are only a means of establishing a smooth and consistent idle, if they weren't there we'd have to adjust the throttle plates which as they are quite big would have a fairly dramatic effect upon engine performance in terms of vibration due to imbalance again.
The system fitted to the bike is quite old fashioned now (out of date) when compared to whats in your latest offerings from the car makers:
At the risk of putting my head on the chopping block the system lacks; the refinement available to this manufacturer that they incorporate into their cars but do not put onto their bikes. Still only using one (possibly two lambda sensors) lambda sensor but with many more controls and ECU monitored sensors. Probably the reason that they do not put best practice onto the bike engines is because its still an old air cooled lump.
Suzuki, Yamaha, Kawasaki and Honda plus Aprilia and now Ducati, all have superior fuel injection when compared to above.
There no doubt my two penn'oth will draw marked criticism but what the heck!
