Main Motorcycle: '01 Triumph Bonneville
Join Date: Sep 2012
After further testing, I have a gut feeling that that the fuel metering by the idle mixture screw is nonlinear. The reason I think this is that because there is a distinct and sudden change in engine character between 1-1.75 turns out to 2.0-2.5 turns out. Immediately, the richer settings produces better throttle response and idling characteristics and less coughs back through the intake and airbox.
Perhaps it's the taper of the needle or the fuel mix requirements of the engine, but I think 2.0-2.5 turns might be the optimal operating range for my 790 engine at least (regardless of jet size, to a point). Thus, I'm going to try the 40 size jets at 2.5 turns out and see how the bike copes.