carb tuning tips
This is an almost completely useless web page, but it
does provide a place to write down some notes and tips I got
from the Factory Pro people when I was decoding some odd carb
behavior. If I write it down here I can throw away the scraps
of paper I've been using.
A handy sparkplug chart.
General:
Do the adjustments in the following order, if you do them in
another order you're going to eventually do them in this order
anyway so you might as well as skip the wasted effort and trust me.
If a problem area gets better when the bike has warmed up
then that area is too lean. If it gets worse, it's too rich.
- Better when warm = too lean, make it richer.
- Worse when warm = too rich, make it leaner.
Main jet:
Test: Top end, high rpm, full throttle, test for maximum power/speed
- richer = larger jet
- leaner = smaller jet
Needle height:
Test: Mid-range, between ~4k and 9k for inline fours, about 1-2k less
for twins
- richer = needle higher, lower clip position
- leaner = needle lower, higher clip position
Pilot jet:
Test: Roll on and part throttle crusing
- richer = larger jet
- leaner = smaller jet
Fuel screws
Test: Best idle after warmed up
- richer = screws out
- leaner = screws in
Float height:
Test: Easy roll on to ~3k RPM and whack the throttle open.
This should be smooth.
- richer = higher float level, lower distance from float to carb surface.
- leaner = lower float level, higher distance from float to carb surface.
remember the carbs are upside down when you do the measurements.