So as to not hijack the TB hose mod thread (see below), I started this thread. While I find the little 650 mill to be very spirited, I dislike the strong engine braking effect and find it often makes for rougher shifting unless being either aggressive (i.e. higher revs), or shifting below 4K in the lower gears. With previous bikes (last street bike was a Triumph Speed Triple), I could leisurely and smoothly up and down shift w/o any clunkyness and allow a long coast off throttle in an urban setting awaiting the light to change.
Engine braking is indeed a function of the motor, but some FI systems keep a small bit of fuel squirting on deceleration to avoid a sudden lean mixture in the catalytic converter. To quote the Sewer Urchin, "That's baad." It used to be done with dashpots on carburetors, now it is done with CPUs.
Engine braking occurs when off (or partly off) throttle, so it is dependent on the amount of air admitted at the throttle bodies. With the tube coupling both TB's at fittings past the throttle plate, some intake air is admitted from the other TB as the vaccum is sequentially balanced between the two via the tube...
So would removing the sub throttles and PAIR tubing as suggested with the airbox mod then cause an decrease in engine braking, but a corresponding increase in backfiring and popping on decel?
With a conventional carb system on my 1996 Triumph Speed Triple, replacing the stock cans with aftermarket slip-ons did increase backfiring until I rejetted richer, so adding fuel with FI at decel makes sense to reduce backfiring. What I do not understand it why there is so much more engine braking with the V than the Speed Triple. RPM and compression ratio (10:01 vs 10.6:01) does not account for all of the difference. My experience with engine brakes (i.e. Jacobs Brake, found on diesel engines) is that the air flow is restricted at decel, braking the engine with back pressure developed with the restricted flow.
If my thinking is not faulty, then there must be something restricting the free flow of air upon decel, has anyone that has done the airbox and sub-throttle mod found a decrease in the engine braking effect on the stock Versys?