Registered Forum User
GTL
Bikes: Ducati 888, Suzuki RG500, Triumph Preunit
Posts: 403
Join Date: Jun 2005
Location: Nottingham
Mood: On the up
As far as I'm aware, spitting back could be due to a lean mixture and/or timing issue. Intermittent problems are always 'fun' to track down.... You seem to have ruled out the most likely suspects but not the RPM and timing sensors as Jools suggests. Might be worth checking air gaps and swapping them around (or trying alternatives if available) and see what happens?
Keith