The question was raised why Yamaha specifically stated do not adjust the
butterflies when syncing the injectors. Although I do not have the official
engineering reason behind the statement, I have given it some thought.
First, being injected, fuel delivery is not dependent on engine vacuum.
Syncing butterflies is compensating/equalizing engine vacuum for the purpose
of fuel delivery. It seems reasonable that some things are constants and some
are variables. The amount of fuel delivered through the injector is a
constant, relative to throttle position. Meaning at any given throttle
setting, the same amount of fuel is being delivered. On carbureted engines,
vacuum affects fuel delivery. I believe the significance of this is that the
injection needs the constant of the butterfly for proper operation. They know
how much fuel they are supplying per throttle opening and know where they
want the butterflies for that amount of fuel. Although it defies conventional
carbureted logic, I take them at their word and assume they knew what they
were doing when they designed the system and wrote the manual on how to
service it. On carbs, sync is most critical for off idle performance. A bike
that has out of sync carbs tends to be sluggish off idle because all
cylinders are not pulling their own weight. Out of sync can also manifest
itself as a hanging idle, which happens when free revving the bike, it takes
an abnormally long time to return to idle. It was mentioned that syncing the
butterflies addressed mid throttle issues. That is true that it could, but
whether the results are quantifiable or not has not been proven. That
remaining an unknown, for me the proper way to sync the injectors is use the
air screws as they recommend. It is airflow into the cylinder that needs to
be adjusted to make sure all cylinders have proper air to fuel mixture. Since
the fuel delivery is constant, adjusting the airflow to compensate for any
deviations in vacuum seems acceptable. As far as setting the air screws at
two turns, it is a round number but what is it based on? Yamaha does not
mention any specs for setting air screws. They tell you to adjust them as
needed to maintain sync. On multi carb or multi injector engines that do not
use cables to connect the aspirators, the necessity of midrange adjustment
diminishes. What comes to mind are some V twin engines with two carbs linked
by cables. However, even on those engines, the best performance obtained is
getting the carbs to open off idle at the same time. I would speculate
adjusting sync at midrange would produce infinitesimal improvements or power
or economy.
As far as six speed transmissions, I agree with J, not worth the effort.
Someone erroneously stated it would be the same as changing the rear
sprocket. This is not true. The six speed is not an overdrive transmission.
Top gear is still a one to one ratio, same as the five speed. The difference
is the ratio of the gears getting to sixth. They are closer together in
ratio. This translates to more shifting, because when you up shift or down
shift, you are not making as big a change in the overall gear ratio. This is
all well and good if you have an engine that has a narrow power band and
cannot effectively pull above or below a narrow RPM range. The GTS engine
configuration and design do not fit that category. Furthermore, putting six
gears where five once were requires the physical width of each gear to be
reduced and average of 20%. This means more load concentration on each tooth.
It is a benefit to have four engagement dogs, but at the expense of decreased
load bearing on the gear teeth. Since we are not dealing with a high
horsepower engine in the GTS, it is entirely possible this will never be an
issue. The reality is, all things in the engineering and design are trade
offs. Yes, an OWO1 made more horsepower and transmitted it through these
gears, but they only had to last a maximum of 200 miles. They were willing to
take the trade off of durability for obtaining the closer ratios needed to
keep the engine operating in the RPM range it had to to make the power it
did. Basically they were having to turn a lot of RPMs to make a lot of power,
and gave up powerband width to get it. Having four dogs instead of three
would indicate they were more concerned with keeping it in gear for 200 miles
than teeth shattering. This is merely fixing the weakest link. The intrinsic
value of having something no one else has is subjective and personal. If it
is important to you, more power to you. On paper and in the real world, a six
speed in a GTS is of no real value and stands a good chance of being a
greater liability because of the increased shifting frequency and decreased
durability.
RSRBOB
