It is important to follow the factory procedure to set the idle speed at 1400 rpm. While working with a local OSSA dealer, I was allowed some brief contact with a factory EFI technician. He admitted that the strange idle-setting procedure is simply because it yields a throttle setting that provides the easiest starting (and had nothing to do with EURO3 compliance). I also learned that OSSA was looking into using a different throttle body that would permit customer alteration of the idle speed.
On my own, using K-Scan, I noticed that the ignition timing changes hugely at the slightest movement of the throttle. It is about 20° BTDC while idling, and jumps to approximately 30° BTDC just off idle (exact behavior is map dependent). This produces exactly the behavior desirable in a trials bike – instant throttle response just off idle.
This is also the reason OSSA says to use no throttle when kickstarting. I have found this to generally be a beneficial practice – but once the engine fires, using a little throttle will encourage it to keep running.
It is a bit difficult to determine, but I believe that at kicking speed the ignition timing is retarded to about 8° BTDC. That is a number that makes sense to me for starting. As the ignition advance increases, there is a higher probability of “kickback” due to combustion pressure increasing enough to prevent rotation past TDC in the running direction.
I have experimented with different initial idle speeds and TPS settings only to find that the factory procedure yields the best power-delivery characteristics. Any increase in the TPS zero-point alters the ignition timing from 20° BTDC to 30° BTDC. This causes a rough idle and potential stalling at inopportune moments. It is possible to reset the TPS to allow an increased idle speed, but with the trade-off of less-than-stellar running elsewhere. Basically, the slow idle was, to me, preferable to imperfect fueling elsewhere.
Since the recommended 1400 rpm idle speed is too low for my liking, I came up with a solution that gives the best of both worlds. See the section on “Idle Air Bypass”.
The engine speed readout in K-Scan is not filtered heavily enough. This causes the reported engine speed to fluctuate greatly while setting the TPS. I always use the engine speed reported by my Trail Tech TTO Tach/Hourmeter instead.