Motorcycle Forum / General / Sportbikes / December 2004

All relative statements. To one unaccustomed to dealing with anything
other than factory fueling your bike does indeed run fine. But to a
trained ear you can hear the lean misfire and certainly feel the crap
throttle response in comparison to richer "jetting". Of course some
companies get it better than others. And the inclusion of catalysts in
the exhaust now means you can use richer fueling whilst still meeting
emissions specs. Just like swtiching to EFI meant you can stay
horribly lean in the testing zone and go rich elsewhere, something a
lot more difficult to tune on carbs.

Really hot days sitting in traffic will send the temp skyward. And
make the engine run rougher. More fuel will cool combustion down and
lower temps.

Complaining of tapping is common amongst the 600 crowd. They all do
that and most owners are newbies on their first bike hyperanalysing
everything to make sure their pride-n-joy is still intact.

A properly set up engine taps. Lower weight = less metal+insulation =
louder engine noises. Then again maybe you're not riding a race
replica 600 and don't know what you're talking about.  Looser
clearances ensure the valve seals shut and develops full compression.
If you bike is stone quiet then consider the fact that your wonderful
motorcycle is not sealing properly and the hot exhaust gasses are
weeping past the seat, toasting it and the valve extra crispy.

Of course right about now I expect someone from the "tight valves"
school of thought to come along and tell me I'm wrong. They'll argue
that closing up the clearance will acutate the valve infintesimally
sooner and thus advance the timing to gain performance. Nevermind that
you can accomplish the same thing by degreeing the cams. This is a
"free" .01 horsepower!

Not necessarily: remember, in the U.S, many bikes are deliberately
leaned-out to meet EPA regs.  Happened all the time with carb'd bikes.

Case in point: my '95 Gixxer.  Cam timing was optimized to minimize
emissions.  I think stock it was 110 degrees intake, 106 exhaust.
This was not optimal for maximum-efficiency burn of the fuel-air
mixture, according to K.C. Gager, the guy who tuned my bike (and other
race bikes: the name's familiar to Bay Area readers).  He had facts
and numbers to back up the position, too.

With slotted cam sprockets, he solved the problem by setting both to
106 degrees, I believe.

Similar was occurring with the stock jetting, solved with a Factory
Stage III kit.

From Roadracing World, I'm reading they're a lot better these days
optimizing both emissions and engine efficiencies with modern engines
and EFI.  Still, the stock numbers might not be optimal.

In any case, if I'm not mistaken the bike in question isn't
fuel-injected anyway.

'-----------------------------------------------------
' Daniel Bannon
' NW WA State, U.S.A.
' 2003 ZX636B Hercusaki, 1999 CBR1100XX
'-----------------------------------------------------