Make a round 2 inch hole in the air box cover besides the stock intake
The stock intake restricts the motor from 6500 rpm and up... (Dyno bench results clearly shows it)
Remove the stock velocity stack (the rubber intake boot or whatever you call it)
Drill out the round brass plug underneath the carb (close to the intake manifold),
make the hole big enough for a self tapping screw and wiggle the plug out.
Be careful not to damage the pilots screws underneath the brass plug while drilling.
Adjust the pilot screws 1/2 turn out from stock setting, anti-clockwise. (stock setting
is around 2 1/2 turns out from fully seated, be careful not to damaged the seat...)
Replace the stock #102.5 main jets with #127.5 Mikuni type "N100/604 Large Round".
Replace the stock #37.5 pilot jets with #35 Mikuni type "N151.067" or "BS30/96" (doesn't matter which).
Shim each throttle needle by 2 pcs of 3 mm stainless steel washer, each is aprox .025 inch thick.
Check the float height, it's very important for slightly off idle and slow cruising. Set the floats to 14.5 mm
measuring from the float bowl and the bottom of the float when the needle valve spring is barely closed
and should not compress the spring at all, just barely seated. Compress the plastic arrangement as the
bowl would do when assembled before you measure the height, it will give false readings otherwise.
The bigger main jets overlap the pilot jet range and because of that the pilots needs to be
smaller in size. The #35/#127.5 setup gives optimum power when the motor has been
warmed up and it's verified by both (countless) Dyno runs and on the road and drag strip
with an air/fuel monitor. Check out all of my Dynorun on the Dynorun page.
My air/fuel ratio with #35/#127.5 and 0.05" shim with pilots screws 1/2 turn out
from stock setting with the stock air filter was:
1/2 - WOT 12.5:1 - max power on the drag strip
1/4 - 1/2 13.5:1 - piston and valve saver in the mountains
1/8 - 1/4 14.5:1 - perfect for highways, good fuel economy
Idle- 1/8 12.0:1 - no spitting, coughing or stumbling at traffic lights
Replace the stock exhaust muffler with a free flowing exhaust since it's strangeling your bike!
This setup was tested with a Kerker K45 bolt-on cannister but anything goes. If you remove the stock
muffler completly it will not affect the result since the elbow pipe itself contains a (LOUD) muffler.
One last note, if you bike coughs and spits back when cold, that normal behaviour when the motor is cold.
That's why they fitted the bike with a choke circuit. Use it. This is normal with a carburated motor, with
fuel injection you don't need a choke - it's built-in into the injections open loop software.