From
Mikuni Carb Tuning Manual :
Open the throttle fully and let the
engine pull for several seconds.
Then, quickly close the throttle to
about the 7/8ths position.
If the engine seems to gain power,
the main jet is too small (lean). Fit a
larger jet.
If the engine hesitates as the
throttle is rolled off, the main jet is
too large. Fit a smaller one.
POOR FULL THROTTLE PERFORMANCE:
(Detonation, flat acceleration,
misfiring.)
Possible causes:
1. One-way tank vents may fail to
allow enough air into the tank to
replace fuel flow at high throttle
openings. The result is a partial
vacuum and fuel starvation.
2. A clogged fuel filter or petcock
screen can result in fuel starvation.
3. A too large or too small main jet
can lead to poor power output.
4. A partially clogged main jet may
allow enough fuel flow for part
throttle operation and yet starve the
engine at full throttle.
5. Air filters can become dirty enough
to restrict air flow and power output.
This is more likely to be a problem
with the stock filter than aftermarket
filters.
