I've been riding my Canadian spec '11 V-650 for a couple months now, in weather ranging from hot and dry to rain, cold, snow and otherwise nasty. I've experienced a noticeable difference in engine response depending on the conditions, and had more than one chance to ponder how the various components of the fuel injection may be working together to sometimes produce crisp, responsive, exhilarating performance. And other times be twitchy to the point that I feel like a new rider.
Of particular interest to me is the often harsh transition from deceleration fuel cut back to fueling when the throttle is opened again. I appreciate that this is a common complaint and has been discussed numerous times. I'd like to approach it from a slightly different angle and welcome your input. I should mention that I have not taken the time to research other forums of Kawasaki 650 engined bikes, so the answers may already be out there. If only I didn't have to sleep...
As far as I can tell, there are a couple components that work together with regard to idle speed and the deceleration fuel cut. The idle speed screw, the throttle bypass screws, and the Throttle Position Sensor are what come to mind as they all are easily adjustable. Intake Air Temperature, Intake Air Pressure and Coolant Temperature sensors are other inputs, but I'd rather not get involved in sending altered signals to the ECU unless absolutely necessary. We know that the factory settings are, at best, "good enough". It would be a rare occasion that a dealership, actually their technicians, would do any better. So, that leaves us enthusiast owners to determine the optimum adjustments, if they exist.
My hope is, with the correct adjustment of the various components, one should be able to have the TPS operating in an optimum range. Signalling Wide Open Throttle, closed throttle, and throttle opening just as they occur. I believe I read that the ECU advances the ignition timing partially based on the TPS signal. This is likely an important factor in the throttle response, and also should be considered. Does anyone have any info on that?
I don't know if it would work or not, but the one thought that has come to mind is to adjust the TPS to narrow it's range. Set the TPS so it just
reads WOT at WOT. Then check the idle TPS reading. If the TPS idle reading is not just
at the high end of the idle range, adjust the idle speed screw to get the desired reading - ignoring the actual idle speed for a moment. Then use the idle bypass screws to adjust the idle speed back to spec, while maintaining a proper vacuum sync.
Is there enough adjustment for this to work? Would narrowing the TPS range be the correct action? Or should one adjust to the wide ends of the TPS range? It would take some effort and I don't know if it would work, but I'd like to find out! What do you think?