By Factory
Pro Tuning
Follow steps in
order....First, dial in:
1.
Top end (full throttle / 7.5k to redline) -
Best Main Jet must be selected before starting
step 2!
Select
Best Main Jet
-
To get the best, most even top end power (full throttle/after 7500
rpm), select the main jet that produces the highest top speed /
pulls hardest at high rpm.
-
If the bike pulls
harder at high rpm when cold and less hard when fully warmed up,
the main jet is too large. Install a smaller main jet and retest
until you find the main jet that pulls the hardest at high rpm
when fully warmed up. This must be done first - before moving on
to the other tuning ranges.
-
If the bike doesn't
pull well at high rpm when cold and gets only slightly better
when fully warmed up, the main jet is too small.
-
In order to properly
tune the midrange and low rpm carburetion, THE MAIN JET MUST
FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
NOTE: Do not pay too much attention to the low-end richness when
you are changing main jets - you still need to be using the main
jets that produce the best power at high rpm. You will deal with
the low-end / cruise later - after step 2.
2.
Midrange (full throttle /5k-7k)
Select best needle clip position
-
To get the best power at full throttle / 5k-7k rpm, adjust the
needle height, after you have already selected the best main jet.
-
If the engine pulls
better or is smoother at full throttle/5k-7k in a full throttle
roll-on starting at <3k when cool but soft and/or rough when at
full operating temperature, it is too rich in the midrange and
the needle should be lowered.
-
If the engine pulls
better when fully warmed up but still not great between 5k-7k,
try raising the needle to richen 5k-7k.
-
If the engine pulls
equally well between 5k-7k when cooler as compared to fully
warmed up, the needle height is probably properly set.
NOTE: Do not pay too much attention to the low-end richness when
you are changing needle clip positions - you still need to be
using the clip position that produces the best full throttle /
5k-7k power in conjunction with the main jets (Step 1) that
produce the best power at high rpm. You will deal with the low-end
/ cruise next.
3.
Low end (full throttle / 2k-3k)
Float height (AKA fuel level &
how to..)
-
To get best low-end power, set float height (fuel level) so that
the engine will accept full throttle, without missing or
stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
-
Float heights, unless
otherwise specified in the installation guide, are measured from
the "gasket surface" of the carb body to the highest part of the
top of the float - with the float tang touching but not
compressing the float valve spring.
-
If the engine has a
"wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that
gets worse as the engine heats up, lower the fuel level by
resetting the float height 1mm greater (if the original was 13mm
- go to 14mm). This will lower the fuel level, making full
throttle / 2k-3k rpm leaner.
-
If the engine is
"dry" and flat between 2k to 3k rpm, raise the fuel level.
-
Example: change float
height from 15mm to 14mm to richen up that area.
REMEMBER, since the main jet WILL affect low speed operation, the
MAIN JET has to be within 1 or 2 sizes of correct before final
float setting.
WARNING: If the engine is left with the fuel level too high,, the
engine may foul plugs on the street and will be "soft" and boggy
at part throttle operation. Adjust Floats to raise/ lower the Fuel
Level.
-
Base settings are usually given if a particular application has a
history of fuel level criticalness. The Fuel level height in the
float bowl affects full throttle/low rpm and, also, richness or
leanness at cruise/low rpm.
-
Reference: a bike that runs cleanly at small throttle openings
when cold, but starts to show signs of richness as it heats up to
full operating temperature, will usually be leaned out enough to
be correct if the fuel level is LOWERED 1mm. Check out and RESET
all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed
problems occur). Needless to say, FUEL LEVEL IS EXTREMELY
IMPORTANT!!!
-
If there are low-end richness problems, even after lowering the
fuel level much more than 1.5mm from our initial settings, check
for needle wear and needle jet (part of the emulsion tube). It is
VERY common for the brass needle jets (in the top of the "emulsion
tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as
little as 5,000 miles. Check them for "oblong" wear - the needle
jet orifice starts out round!
4.
Idle and low rpm cruise
Fuel Screw setting (AKA mixture screws)
-
Set for smoothest
idle and 2nd gear, 4k rpm, steady state cruise operation. Set
mixture screws at recommended settings, as a starting point. For
smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8
throttle high rpm operation.
-
Pilot fuel mixture
screw settings, float level (but, you've "fixed" the fuel level
in Step 3 above - which you have already done!) AND pilot jet
size are the primary sources of mixture delivery during 4000 rpm
steady state cruise operation.
-
If lean surging is
encountered, richen mixture screws (turn out) in 1/2 turn
increments. Alternative pilot jets are supplied when normally
required.
-
Pilot fuel mixture
screw settings, float level and pilot jet size also affect
high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause
surging problems when the engine is operated at high rpm at
small throttle openings! Opening the mixture screws and/or
increasing pilot jet size will usually cure the problem.
NOTE: A rich problem gets worse as the engine heats up.
-
If the throttle is
lightly "blipped" at idle, and the rpm drops below the set idle
speed, then rises up to the set idle speed, the low speed
mixture screws are probably set too rich: try 1/2 turn in, to
lean the idle mixture.
NOTE: A lean problem gets better as the engine heats up.
-
If the throttle is
lightly "blipped" at idle, and the rpm "hangs up" before
dropping to the set idle speed, and there are no intake leaks
and the idle speed is set at less than 1000 rpm, the mixture
screws are probably too lean: try 1/2 turn out, to richen
mixture. Be sure there are no intake leaks and the idle speed is
set at less than 1000 rpm!
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